diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4d8c8ded3a..3878b52cb7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@
 - Fix: 通知の範囲指定の設定項目が必要ない通知設定でも範囲指定の設定がでている問題を修正
 - Fix: Turnstileが失敗・期限切れした際にも成功扱いとなってしまう問題を修正  
   (Cherry-picked from https://github.com/MisskeyIO/misskey/pull/768)
+- Enhance: 投稿フォームでEscキーを押したときIME入力中ならフォームを閉じないように（ #10866 ）  
 
 ### Server
 -
diff --git a/packages/frontend/src/components/MkPostForm.vue b/packages/frontend/src/components/MkPostForm.vue
index 76a6e4212a..b6b80082d3 100644
--- a/packages/frontend/src/components/MkPostForm.vue
+++ b/packages/frontend/src/components/MkPostForm.vue
@@ -65,10 +65,10 @@ SPDX-License-Identifier: AGPL-3.0-only
 		</div>
 	</div>
 	<MkInfo v-if="hasNotSpecifiedMentions" warn :class="$style.hasNotSpecifiedMentions">{{ i18n.ts.notSpecifiedMentionWarning }} - <button class="_textButton" @click="addMissingMention()">{{ i18n.ts.add }}</button></MkInfo>
-	<input v-show="useCw" ref="cwInputEl" v-model="cw" :class="$style.cw" :placeholder="i18n.ts.annotation" @keydown="onKeydown">
+	<input v-show="useCw" ref="cwInputEl" v-model="cw" :class="$style.cw" :placeholder="i18n.ts.annotation" @keydown="onKeydown" @keyup="onKeyup" @compositionend="onCompositionEnd">
 	<div :class="[$style.textOuter, { [$style.withCw]: useCw }]">
 		<div v-if="channel" :class="$style.colorBar" :style="{ background: channel.color }"></div>
-		<textarea ref="textareaEl" v-model="text" :class="[$style.text]" :disabled="posting || posted" :readonly="textAreaReadOnly" :placeholder="placeholder" data-cy-post-form-text @keydown="onKeydown" @paste="onPaste" @compositionupdate="onCompositionUpdate" @compositionend="onCompositionEnd"/>
+		<textarea ref="textareaEl" v-model="text" :class="[$style.text]" :disabled="posting || posted" :readonly="textAreaReadOnly" :placeholder="placeholder" data-cy-post-form-text @keydown="onKeydown" @keyup="onKeyup" @paste="onPaste" @compositionupdate="onCompositionUpdate" @compositionend="onCompositionEnd"/>
 		<div v-if="maxTextLength - textLength < 100" :class="['_acrylic', $style.textCount, { [$style.textOver]: textLength > maxTextLength }]">{{ maxTextLength - textLength }}</div>
 	</div>
 	<input v-show="withHashtags" ref="hashtagsInputEl" v-model="hashtags" :class="$style.hashtags" :placeholder="i18n.ts.hashtags" list="hashtags">
@@ -201,6 +201,7 @@ const recentHashtags = ref(JSON.parse(miLocalStorage.getItem('hashtags') ?? '[]'
 const imeText = ref('');
 const showingOptions = ref(false);
 const textAreaReadOnly = ref(false);
+const justEndedComposition = ref(false);
 
 const draftKey = computed((): string => {
 	let key = props.channel ? `channel:${props.channel.id}` : '';
@@ -573,7 +574,13 @@ function clear() {
 function onKeydown(ev: KeyboardEvent) {
 	if (ev.key === 'Enter' && (ev.ctrlKey || ev.metaKey) && canPost.value) post();
 
-	if (ev.key === 'Escape') emit('esc');
+	// justEndedComposition.value is for Safari, which keyDown occurs after compositionend.
+	// ev.isComposing is for another browsers.
+	if (ev.key === 'Escape' && !justEndedComposition.value && !ev.isComposing) emit('esc');
+}
+
+function onKeyup(ev: KeyboardEvent) {
+	justEndedComposition.value = false;
 }
 
 function onCompositionUpdate(ev: CompositionEvent) {
@@ -582,6 +589,7 @@ function onCompositionUpdate(ev: CompositionEvent) {
 
 function onCompositionEnd(ev: CompositionEvent) {
 	imeText.value = '';
+	justEndedComposition.value = true;
 }
 
 async function onPaste(ev: ClipboardEvent) {