diff --git a/app/components/model-types/ConversionModal.vue b/app/components/model-types/ConversionModal.vue
new file mode 100644
index 0000000..22ba69d
--- /dev/null
+++ b/app/components/model-types/ConversionModal.vue
@@ -0,0 +1,172 @@
+<template>
+  <dialog class="modal" :class="{ 'modal-open': open }">
+    <div class="modal-box max-w-2xl">
+      <h3 class="text-lg font-bold text-base-content">
+        Convertir la catégorie
+      </h3>
+
+      <!-- Loading state -->
+      <div v-if="checking" class="mt-4 flex items-center gap-2 text-sm text-info">
+        <span class="loading loading-spinner loading-sm" aria-hidden="true"></span>
+        Vérification de la conversion…
+      </div>
+
+      <!-- Error state -->
+      <div v-else-if="checkError" class="mt-4 text-sm text-error">
+        {{ checkError }}
+      </div>
+
+      <!-- Blocked state -->
+      <template v-else-if="checkResult && !checkResult.canConvert">
+        <p class="mt-3 text-sm text-base-content/70">
+          La conversion de « {{ modelType?.name }} » est impossible pour les raisons suivantes :
+        </p>
+        <ul class="mt-3 space-y-1">
+          <li
+            v-for="(blocker, i) in checkResult.blockers"
+            :key="i"
+            class="flex items-start gap-2 rounded-lg border border-error/20 bg-error/5 px-3 py-2 text-sm text-error"
+          >
+            <IconLucideCircleX class="mt-0.5 h-4 w-4 shrink-0" aria-hidden="true" />
+            {{ blocker }}
+          </li>
+        </ul>
+      </template>
+
+      <!-- Eligible state -->
+      <template v-else-if="checkResult && checkResult.canConvert">
+        <div class="mt-3 rounded-lg border border-warning/20 bg-warning/5 px-4 py-3">
+          <p class="text-sm font-medium text-warning">
+            {{ directionLabel }}
+          </p>
+          <p class="mt-1 text-sm text-base-content/70">
+            {{ checkResult.itemCount }} élément(s) seront convertis. Cette opération est irréversible.
+          </p>
+        </div>
+
+        <div
+          v-if="checkResult.names.length > 0"
+          class="mt-3 rounded-xl border border-base-200 bg-base-100"
+        >
+          <p class="px-4 pt-3 text-sm font-medium text-base-content/70">
+            Éléments concernés :
+          </p>
+          <ul class="max-h-48 divide-y divide-base-200 overflow-y-auto px-4 pb-3">
+            <li
+              v-for="(name, i) in checkResult.names"
+              :key="i"
+              class="py-1.5 text-sm text-base-content"
+            >
+              {{ name }}
+            </li>
+          </ul>
+        </div>
+
+        <div v-if="convertError" class="mt-3 text-sm text-error">
+          {{ convertError }}
+        </div>
+      </template>
+
+      <div class="modal-action">
+        <button
+          type="button"
+          class="btn"
+          :disabled="converting"
+          @click="emit('close')"
+        >
+          Fermer
+        </button>
+        <button
+          v-if="checkResult?.canConvert"
+          type="button"
+          class="btn btn-warning"
+          :disabled="converting"
+          @click="doConvert"
+        >
+          <span v-if="converting" class="loading loading-spinner loading-sm" aria-hidden="true"></span>
+          Convertir
+        </button>
+      </div>
+    </div>
+  </dialog>
+</template>
+
+<script setup lang="ts">
+import { ref, watch } from 'vue';
+import IconLucideCircleX from '~icons/lucide/circle-x';
+import {
+  checkConversion,
+  convertCategory,
+  type ConversionCheck,
+  type ModelType,
+} from '~/services/modelTypes';
+
+const props = defineProps<{
+  open: boolean;
+  modelType: ModelType | null;
+}>();
+
+const emit = defineEmits<{
+  (e: 'close'): void;
+  (e: 'converted'): void;
+}>();
+
+const checking = ref(false);
+const checkError = ref<string | null>(null);
+const checkResult = ref<ConversionCheck | null>(null);
+const converting = ref(false);
+const convertError = ref<string | null>(null);
+
+const directionLabel = computed(() => {
+  if (!checkResult.value) return '';
+  return checkResult.value.direction === 'piece_to_component'
+    ? 'Conversion : Catégorie de pièce → Catégorie de composant'
+    : 'Conversion : Catégorie de composant → Catégorie de pièce';
+});
+
+watch(
+  () => props.open,
+  async (isOpen) => {
+    if (!isOpen || !props.modelType) {
+      return;
+    }
+
+    checking.value = true;
+    checkError.value = null;
+    checkResult.value = null;
+    convertError.value = null;
+
+    try {
+      checkResult.value = await checkConversion(props.modelType.id);
+    } catch (err: any) {
+      checkError.value =
+        err?.data?.message || err?.message || 'Erreur lors de la vérification.';
+    } finally {
+      checking.value = false;
+    }
+  },
+);
+
+const doConvert = async () => {
+  if (!props.modelType) return;
+
+  converting.value = true;
+  convertError.value = null;
+
+  try {
+    const result = await convertCategory(props.modelType.id);
+
+    if (!result.success) {
+      convertError.value = result.error || 'La conversion a échoué.';
+      return;
+    }
+
+    emit('converted');
+  } catch (err: any) {
+    convertError.value =
+      err?.data?.message || err?.message || 'Erreur lors de la conversion.';
+  } finally {
+    converting.value = false;
+  }
+};
+</script>
diff --git a/app/components/model-types/ManagementView.vue b/app/components/model-types/ManagementView.vue
index 86f182a..3b96f39 100644
--- a/app/components/model-types/ManagementView.vue
+++ b/app/components/model-types/ManagementView.vue
@@ -29,12 +29,21 @@
       :total="total"
       :limit="limit"
       :offset="offset"
+      :category="selectedCategory"
       @related="openRelatedModal"
       @edit="openEditPage"
       @delete="confirmDelete"
+      @convert="openConversionModal"
       @update:offset="onOffsetChange"
     />
 
+    <ModelTypesConversionModal
+      :open="conversionModalOpen"
+      :model-type="conversionTarget"
+      @close="closeConversionModal"
+      @converted="onConverted"
+    />
+
     <dialog class="modal" :class="{ 'modal-open': relatedModalOpen }">
       <div class="modal-box max-w-3xl">
         <h3 class="text-lg font-bold text-base-content">
@@ -96,6 +105,7 @@ import { computed, onBeforeUnmount, onMounted, ref, watch, type Ref } from "vue"
 import { useHead, useRouter } from "#imports";
 import ModelTypesToolbar from "~/components/model-types/Toolbar.vue";
 import ModelTypesTable from "~/components/model-types/Table.vue";
+import ModelTypesConversionModal from "~/components/model-types/ConversionModal.vue";
 import { useApi } from "~/composables/useApi";
 import { useUrlState } from "~/composables/useUrlState";
 import { extractCollection } from "~/shared/utils/apiHelpers";
@@ -484,6 +494,26 @@ const closeRelatedModal = () => {
   relatedModalOpen.value = false;
 };
 
+const conversionModalOpen = ref(false);
+const conversionTarget = ref<ModelType | null>(null);
+
+const openConversionModal = (item: ModelType) => {
+  conversionTarget.value = item;
+  conversionModalOpen.value = true;
+};
+
+const closeConversionModal = () => {
+  conversionModalOpen.value = false;
+};
+
+const onConverted = () => {
+  conversionModalOpen.value = false;
+  invalidateEntityTypeCache("PIECE");
+  invalidateEntityTypeCache("COMPONENT");
+  showSuccess("Catégorie convertie avec succès.");
+  refresh();
+};
+
 watch(
   () => searchInput.value,
   (value) => {
diff --git a/app/components/model-types/Table.vue b/app/components/model-types/Table.vue
index 2609555..f119901 100644
--- a/app/components/model-types/Table.vue
+++ b/app/components/model-types/Table.vue
@@ -48,6 +48,15 @@
                 <button type="button" class="btn btn-ghost btn-sm" @click="emit('related', item)">
                   Liés
                 </button>
+                <button
+                  v-if="showConvertButton"
+                  type="button"
+                  class="btn btn-ghost btn-sm text-warning"
+                  @click="emit('convert', item)"
+                >
+                  <IconLucideArrowLeftRight class="h-4 w-4" aria-hidden="true" />
+                  Convertir
+                </button>
                 <button type="button" class="btn btn-ghost btn-sm" @click="emit('edit', item)">
                   Éditer
                 </button>
@@ -78,6 +87,15 @@
             <button type="button" class="btn btn-ghost btn-sm" @click="emit('related', item)">
               Liés
             </button>
+            <button
+              v-if="showConvertButton"
+              type="button"
+              class="btn btn-ghost btn-sm text-warning"
+              @click="emit('convert', item)"
+            >
+              <IconLucideArrowLeftRight class="h-4 w-4" aria-hidden="true" />
+              Convertir
+            </button>
             <button type="button" class="btn btn-ghost btn-sm" @click="emit('edit', item)">
               Éditer
             </button>
@@ -118,6 +136,7 @@
 <script setup lang="ts">
 import { computed } from 'vue';
 import IconLucideInbox from '~icons/lucide/inbox';
+import IconLucideArrowLeftRight from '~icons/lucide/arrow-left-right';
 import type { ModelType, ModelCategory } from '~/services/modelTypes';
 
 const props = defineProps<{
@@ -126,15 +145,21 @@ const props = defineProps<{
   total: number;
   limit: number;
   offset: number;
+  category?: ModelCategory;
 }>();
 
 const emit = defineEmits<{
   (e: 'related', item: ModelType): void;
   (e: 'edit', item: ModelType): void;
   (e: 'delete', item: ModelType): void;
+  (e: 'convert', item: ModelType): void;
   (e: 'update:offset', offset: number): void;
 }>();
 
+const showConvertButton = computed(() =>
+  props.category === 'PIECE' || props.category === 'COMPONENT',
+);
+
 const categoryDictionary: Record<ModelCategory, string> = {
   COMPONENT: 'Composants',
   PIECE: 'Pièces',
diff --git a/app/services/modelTypes.ts b/app/services/modelTypes.ts
index 2a34e7a..772a81a 100644
--- a/app/services/modelTypes.ts
+++ b/app/services/modelTypes.ts
@@ -219,3 +219,33 @@ export function getModelType(id: string, opts: { signal?: AbortSignal } = {}) {
     signal: opts.signal,
   })).then(normalizeModelType);
 }
+
+export interface ConversionCheck {
+  canConvert: boolean;
+  direction: 'piece_to_component' | 'component_to_piece' | null;
+  itemCount: number;
+  names: string[];
+  blockers: string[];
+}
+
+export interface ConversionResult {
+  success: boolean;
+  convertedCount: number;
+  error?: string | null;
+}
+
+export function checkConversion(id: string, opts: { signal?: AbortSignal } = {}) {
+  const requestFetch = useRequestFetch();
+  return requestFetch<ConversionCheck>(`${ENDPOINT}/${id}/conversion-check`, createOptions({
+    method: 'GET',
+    signal: opts.signal,
+  }));
+}
+
+export function convertCategory(id: string, opts: { signal?: AbortSignal } = {}) {
+  const requestFetch = useRequestFetch();
+  return requestFetch<ConversionResult>(`${ENDPOINT}/${id}/convert`, createOptions({
+    method: 'POST',
+    signal: opts.signal,
+  }));
+}