diff --git a/src/modules/activities/components/CategorySelector.vue b/src/modules/activities/components/CategorySelector.vue
new file mode 100644
index 0000000..5acb3f8
--- /dev/null
+++ b/src/modules/activities/components/CategorySelector.vue
@@ -0,0 +1,45 @@
+<script setup lang="ts">
+import { useI18n } from 'vue-i18n'
+import { Badge } from '@/components/ui/badge'
+import type { ActivityCategory } from '../types/category'
+import { ALL_CATEGORIES } from '../types/category'
+
+const props = defineProps<{
+  modelValue: ActivityCategory[]
+}>()
+
+const emit = defineEmits<{
+  'update:modelValue': [value: ActivityCategory[]]
+}>()
+
+const { t } = useI18n()
+
+function toggle(cat: ActivityCategory) {
+  const current = [...props.modelValue]
+  const idx = current.indexOf(cat)
+  if (idx >= 0) {
+    current.splice(idx, 1)
+  } else {
+    current.push(cat)
+  }
+  emit('update:modelValue', current)
+}
+
+function label(cat: ActivityCategory): string {
+  return t(`activities.categories.${cat}`, cat)
+}
+</script>
+
+<template>
+  <div class="flex flex-wrap gap-1.5">
+    <Badge
+      v-for="cat in ALL_CATEGORIES"
+      :key="cat"
+      :variant="modelValue.includes(cat) ? 'default' : 'outline'"
+      class="cursor-pointer text-xs select-none hover:opacity-80 transition-opacity"
+      @click="toggle(cat)"
+    >
+      {{ label(cat) }}
+    </Badge>
+  </div>
+</template>
diff --git a/src/modules/activities/components/CreateActivityDialog.vue b/src/modules/activities/components/CreateActivityDialog.vue
new file mode 100644
index 0000000..0c6935a
--- /dev/null
+++ b/src/modules/activities/components/CreateActivityDialog.vue
@@ -0,0 +1,270 @@
+<script setup lang="ts">
+import { ref, computed } from 'vue'
+import { useI18n } from 'vue-i18n'
+import { useForm } from 'vee-validate'
+import { toTypedSchema } from '@vee-validate/zod'
+import * as z from 'zod'
+import {
+  Dialog, DialogContent, DialogHeader, DialogTitle, DialogDescription,
+} from '@/components/ui/dialog'
+import {
+  FormControl, FormField, FormItem, FormLabel, FormMessage,
+} from '@/components/ui/form'
+import { Input } from '@/components/ui/input'
+import { Textarea } from '@/components/ui/textarea'
+import { Button } from '@/components/ui/button'
+import { CalendarPlus } from 'lucide-vue-next'
+import { useAuth } from '@/composables/useAuthService'
+import { tryInjectService, SERVICE_TOKENS } from '@/core/di-container'
+import type { ActivitiesNostrService } from '../services/ActivitiesNostrService'
+import type { CalendarTimeEvent } from '../types/nip52'
+import type { ActivityCategory } from '../types/category'
+import CategorySelector from './CategorySelector.vue'
+import LocationPicker from './LocationPicker.vue'
+import { toast } from 'vue-sonner'
+
+defineProps<{
+  isOpen: boolean
+}>()
+
+const emit = defineEmits<{
+  'update:isOpen': [value: boolean]
+  'created': []
+}>()
+
+const { t } = useI18n()
+const { currentUser } = useAuth()
+
+const isPublishing = ref(false)
+const selectedCategories = ref<ActivityCategory[]>([])
+const location = ref('')
+
+const formSchema = toTypedSchema(z.object({
+  title: z.string().min(1, 'Title is required').max(200),
+  summary: z.string().max(500).optional(),
+  description: z.string().min(1, 'Description is required').max(5000),
+  startDate: z.string().min(1, 'Start date is required'),
+  startTime: z.string().min(1, 'Start time is required'),
+  endDate: z.string().optional(),
+  endTime: z.string().optional(),
+  image: z.string().url('Must be a valid URL').optional().or(z.literal('')),
+}))
+
+const form = useForm({
+  validationSchema: formSchema,
+  initialValues: {
+    title: '',
+    summary: '',
+    description: '',
+    startDate: '',
+    startTime: '',
+    endDate: '',
+    endTime: '',
+    image: '',
+  },
+})
+
+const isFormValid = computed(() => form.meta.value.valid)
+
+const onSubmit = form.handleSubmit(async (values) => {
+  const nostrService = tryInjectService<ActivitiesNostrService>(SERVICE_TOKENS.ACTIVITIES_NOSTR_SERVICE)
+  if (!nostrService) {
+    toast.error('Activities service not available')
+    return
+  }
+
+  const signingKey = currentUser.value?.prvkey
+  if (!signingKey) {
+    toast.error('Signing key not available. Please log in again.')
+    return
+  }
+
+  isPublishing.value = true
+
+  try {
+    // Build unix timestamps
+    const startTimestamp = Math.floor(new Date(`${values.startDate}T${values.startTime}`).getTime() / 1000)
+    let endTimestamp: number | undefined
+    if (values.endDate && values.endTime) {
+      endTimestamp = Math.floor(new Date(`${values.endDate}T${values.endTime}`).getTime() / 1000)
+    }
+
+    // Generate a unique d-tag
+    const dTag = `${Date.now()}-${Math.random().toString(36).slice(2, 8)}`
+
+    const eventData: Partial<CalendarTimeEvent> = {
+      dTag,
+      title: values.title,
+      summary: values.summary || undefined,
+      content: values.description,
+      image: values.image || undefined,
+      start: startTimestamp,
+      end: endTimestamp,
+      startTzid: Intl.DateTimeFormat().resolvedOptions().timeZone,
+      location: location.value || undefined,
+      hashtags: selectedCategories.value,
+    }
+
+    const result = await nostrService.publishCalendarEvent(eventData, signingKey)
+
+    if (result.success > 0) {
+      toast.success(`Activity published to ${result.success} relay${result.success > 1 ? 's' : ''}`)
+      emit('created')
+      handleClose()
+    } else {
+      toast.error('Failed to publish to any relay')
+    }
+  } catch (err) {
+    console.error('Failed to publish activity:', err)
+    toast.error(err instanceof Error ? err.message : 'Failed to publish activity')
+  } finally {
+    isPublishing.value = false
+  }
+})
+
+function handleClose() {
+  emit('update:isOpen', false)
+  form.resetForm()
+  selectedCategories.value = []
+  location.value = ''
+}
+</script>
+
+<template>
+  <Dialog :open="isOpen" @update:open="handleClose">
+    <DialogContent class="sm:max-w-[550px] max-h-[90vh] overflow-y-auto">
+      <DialogHeader>
+        <DialogTitle class="flex items-center gap-2">
+          <CalendarPlus class="w-5 h-5" />
+          {{ t('activities.createNew') }}
+        </DialogTitle>
+        <DialogDescription>
+          Publish a new activity to Nostr relays
+        </DialogDescription>
+      </DialogHeader>
+
+      <form @submit="onSubmit" class="space-y-4 py-2">
+        <!-- Title -->
+        <FormField v-slot="{ componentField }" name="title">
+          <FormItem>
+            <FormLabel>Title *</FormLabel>
+            <FormControl>
+              <Input placeholder="e.g. Marché de Noël de Foix" v-bind="componentField" :disabled="isPublishing" />
+            </FormControl>
+            <FormMessage />
+          </FormItem>
+        </FormField>
+
+        <!-- Summary -->
+        <FormField v-slot="{ componentField }" name="summary">
+          <FormItem>
+            <FormLabel>Summary</FormLabel>
+            <FormControl>
+              <Input placeholder="Brief one-line description" v-bind="componentField" :disabled="isPublishing" />
+            </FormControl>
+            <FormMessage />
+          </FormItem>
+        </FormField>
+
+        <!-- Description -->
+        <FormField v-slot="{ componentField }" name="description">
+          <FormItem>
+            <FormLabel>Description *</FormLabel>
+            <FormControl>
+              <Textarea
+                placeholder="Full details about the activity..."
+                v-bind="componentField"
+                :disabled="isPublishing"
+                rows="4"
+              />
+            </FormControl>
+            <FormMessage />
+          </FormItem>
+        </FormField>
+
+        <!-- Start date/time -->
+        <div class="grid grid-cols-2 gap-3">
+          <FormField v-slot="{ componentField }" name="startDate">
+            <FormItem>
+              <FormLabel>Start date *</FormLabel>
+              <FormControl>
+                <Input type="date" v-bind="componentField" :disabled="isPublishing" />
+              </FormControl>
+              <FormMessage />
+            </FormItem>
+          </FormField>
+
+          <FormField v-slot="{ componentField }" name="startTime">
+            <FormItem>
+              <FormLabel>Start time *</FormLabel>
+              <FormControl>
+                <Input type="time" v-bind="componentField" :disabled="isPublishing" />
+              </FormControl>
+              <FormMessage />
+            </FormItem>
+          </FormField>
+        </div>
+
+        <!-- End date/time -->
+        <div class="grid grid-cols-2 gap-3">
+          <FormField v-slot="{ componentField }" name="endDate">
+            <FormItem>
+              <FormLabel>End date</FormLabel>
+              <FormControl>
+                <Input type="date" v-bind="componentField" :disabled="isPublishing" />
+              </FormControl>
+              <FormMessage />
+            </FormItem>
+          </FormField>
+
+          <FormField v-slot="{ componentField }" name="endTime">
+            <FormItem>
+              <FormLabel>End time</FormLabel>
+              <FormControl>
+                <Input type="time" v-bind="componentField" :disabled="isPublishing" />
+              </FormControl>
+              <FormMessage />
+            </FormItem>
+          </FormField>
+        </div>
+
+        <!-- Location -->
+        <LocationPicker
+          v-model="location"
+          :disabled="isPublishing"
+        />
+
+        <!-- Categories -->
+        <div class="space-y-1.5">
+          <label class="text-sm font-medium">Categories</label>
+          <CategorySelector v-model="selectedCategories" />
+        </div>
+
+        <!-- Image URL -->
+        <FormField v-slot="{ componentField }" name="image">
+          <FormItem>
+            <FormLabel>Image URL</FormLabel>
+            <FormControl>
+              <Input
+                placeholder="https://example.com/image.jpg"
+                v-bind="componentField"
+                :disabled="isPublishing"
+              />
+            </FormControl>
+            <FormMessage />
+          </FormItem>
+        </FormField>
+
+        <!-- Submit -->
+        <Button
+          type="submit"
+          :disabled="isPublishing || !isFormValid"
+          class="w-full"
+        >
+          <span v-if="isPublishing" class="animate-spin mr-2">⚡</span>
+          {{ isPublishing ? 'Publishing...' : 'Publish Activity' }}
+        </Button>
+      </form>
+    </DialogContent>
+  </Dialog>
+</template>
diff --git a/src/modules/activities/components/LocationPicker.vue b/src/modules/activities/components/LocationPicker.vue
new file mode 100644
index 0000000..774a507
--- /dev/null
+++ b/src/modules/activities/components/LocationPicker.vue
@@ -0,0 +1,34 @@
+<script setup lang="ts">
+import { Input } from '@/components/ui/input'
+import { Label } from '@/components/ui/label'
+import { MapPin } from 'lucide-vue-next'
+
+defineProps<{
+  modelValue: string
+  placeholder?: string
+  disabled?: boolean
+}>()
+
+const emit = defineEmits<{
+  'update:modelValue': [value: string]
+}>()
+</script>
+
+<template>
+  <div class="space-y-1.5">
+    <Label class="text-sm font-medium">Location</Label>
+    <div class="relative">
+      <MapPin class="absolute left-3 top-1/2 -translate-y-1/2 w-4 h-4 text-muted-foreground" />
+      <Input
+        :model-value="modelValue"
+        @update:model-value="emit('update:modelValue', $event as string)"
+        :placeholder="placeholder ?? 'e.g. Salle des fêtes, Foix, Ariège'"
+        :disabled="disabled"
+        class="pl-9"
+      />
+    </div>
+    <p class="text-xs text-muted-foreground">
+      Enter the venue name and address
+    </p>
+  </div>
+</template>
diff --git a/src/modules/activities/services/ActivitiesNostrService.ts b/src/modules/activities/services/ActivitiesNostrService.ts
index 8f9008e..2215908 100644
--- a/src/modules/activities/services/ActivitiesNostrService.ts
+++ b/src/modules/activities/services/ActivitiesNostrService.ts
@@ -1,5 +1,5 @@
 import { BaseService } from '@/core/base/BaseService'
-import type { Event as NostrEvent } from 'nostr-tools'
+import { finalizeEvent, type Event as NostrEvent, type EventTemplate } from 'nostr-tools'
 import type { SubscriptionConfig } from '@/modules/base/nostr/relay-hub'
 import {
   NIP52_KINDS,
@@ -107,23 +107,28 @@ export class ActivitiesNostrService extends BaseService {
 
   /**
    * Publish a NIP-52 time-based calendar event.
+   * Requires an authenticated user with a signing key.
    */
   async publishCalendarEvent(
-    eventData: Partial<CalendarTimeEvent>
+    eventData: Partial<CalendarTimeEvent>,
+    signingKeyHex: string
   ): Promise<{ success: number; total: number }> {
     if (!this.relayHub) {
       throw new Error('RelayHub not available')
     }
 
     const tags = buildCalendarTimeEventTags(eventData)
-    const eventTemplate = {
+    const template: EventTemplate = {
       kind: NIP52_KINDS.CALENDAR_TIME_EVENT,
       created_at: Math.floor(Date.now() / 1000),
       content: eventData.content ?? '',
       tags,
     }
 
-    return await this.relayHub.publishEvent(eventTemplate)
+    const privkeyBytes = hexToUint8Array(signingKeyHex)
+    const signedEvent = finalizeEvent(template, privkeyBytes)
+
+    return await this.relayHub.publishEvent(signedEvent)
   }
 
   /**
@@ -161,10 +166,17 @@ export class ActivitiesNostrService extends BaseService {
   }
 
   protected override async onDispose(): Promise<void> {
-    // Clean up all active subscriptions
     for (const unsub of this.activeUnsubscribes) {
       unsub()
     }
     this.activeUnsubscribes = []
   }
 }
+
+function hexToUint8Array(hex: string): Uint8Array {
+  const bytes = new Uint8Array(hex.length / 2)
+  for (let i = 0; i < hex.length; i += 2) {
+    bytes[i / 2] = parseInt(hex.substr(i, 2), 16)
+  }
+  return bytes
+}
diff --git a/src/modules/activities/views/ActivitiesPage.vue b/src/modules/activities/views/ActivitiesPage.vue
index f07e21f..f5f41ca 100644
--- a/src/modules/activities/views/ActivitiesPage.vue
+++ b/src/modules/activities/views/ActivitiesPage.vue
@@ -10,8 +10,10 @@ import {
   CollapsibleContent,
   CollapsibleTrigger,
 } from '@/components/ui/collapsible'
-import { RefreshCw, Search, SlidersHorizontal, ChevronDown } from 'lucide-vue-next'
+import { RefreshCw, Search, SlidersHorizontal, ChevronDown, Plus } from 'lucide-vue-next'
+import { useAuth } from '@/composables/useAuthService'
 import { useActivities } from '../composables/useActivities'
+import CreateActivityDialog from '../components/CreateActivityDialog.vue'
 import TemporalFilterBar from '../components/TemporalFilterBar.vue'
 import CategoryFilterBar from '../components/CategoryFilterBar.vue'
 import DatePickerStrip from '../components/DatePickerStrip.vue'
@@ -20,6 +22,9 @@ import type { Activity } from '../types/activity'
 
 const router = useRouter()
 const { t } = useI18n()
+const { isAuthenticated } = useAuth()
+
+const showCreateDialog = ref(false)
 
 const {
   activities,
@@ -62,6 +67,14 @@ function handleRefresh() {
         </h1>
       </div>
       <div class="flex gap-2 sm:flex-shrink-0">
+        <Button
+          v-if="isAuthenticated"
+          size="sm"
+          @click="showCreateDialog = true"
+        >
+          <Plus class="w-4 h-4 mr-1.5" />
+          {{ t('activities.createNew') }}
+        </Button>
         <Button variant="outline" size="sm" @click="handleRefresh" :disabled="isLoading">
           <RefreshCw class="w-4 h-4 mr-1.5" :class="{ 'animate-spin': isLoading }" />
           Refresh
@@ -156,5 +169,11 @@ function handleRefresh() {
         />
       </TabsContent>
     </Tabs>
+
+    <!-- Create Activity Dialog -->
+    <CreateActivityDialog
+      v-model:is-open="showCreateDialog"
+      @created="handleRefresh"
+    />
   </div>
 </template>