diff --git a/.reasonix/desktop-topic-titles.json b/.reasonix/desktop-topic-titles.json
index cc4abdf..fe7cd63 100644
--- a/.reasonix/desktop-topic-titles.json
+++ b/.reasonix/desktop-topic-titles.json
@@ -37,5 +37,5 @@
   "topic_20260707-092711_af706c3fcc7e435e": "帮我检查一下app.vue里的too…",
   "topic_20260707-095503_bf879b65e4666516": "帮我移除markdownEditor…",
   "topic_20260708-020616_9ab54d98daf65053": "帮我分析一下现在的markdownE…",
-  "topic_20260708-093419_71d1fea2e4b5a40f": "新的会话"
+  "topic_20260708-093419_71d1fea2e4b5a40f": "src/components/Dir…"
 }
\ No newline at end of file
diff --git a/src/components/DirectorySidebar.vue b/src/components/DirectorySidebar.vue
index 548ef8f..2e6c8f8 100644
--- a/src/components/DirectorySidebar.vue
+++ b/src/components/DirectorySidebar.vue
@@ -67,17 +67,76 @@ const rootEntry = computed<DirEntry | null>(() => {
 // ---- sidebar view mode ----
 type ViewMode = "folder" | "search" | "setting";
 const activeView = ref<ViewMode>("folder");
-const expanded = ref(true);
+
+// ---- sidebar resize ----
+const MIN_SIDEBAR_WIDTH = 180;
+const MAX_SIDEBAR_WIDTH = 500;
+const COLLAPSED_WIDTH = 48;
+const DEFAULT_EXPANDED_WIDTH = 288;
+
+const sidebarWidth = ref(DEFAULT_EXPANDED_WIDTH);
+const lastExpandedWidth = ref(DEFAULT_EXPANDED_WIDTH);
+const isResizing = ref(false);
+const isCollapsed = computed(() => sidebarWidth.value <= COLLAPSED_WIDTH);
+
+function expand() {
+  sidebarWidth.value = lastExpandedWidth.value;
+}
+
+function collapse() {
+  sidebarWidth.value = COLLAPSED_WIDTH;
+}
+
+function toggleCollapse() {
+  if (isCollapsed.value) {
+    expand();
+  } else {
+    collapse();
+  }
+}
 
 function switchView(view: ViewMode) {
   if (activeView.value === view) {
-    expanded.value = !expanded.value;
+    toggleCollapse();
   } else {
     activeView.value = view;
-    expanded.value = true;
+    if (isCollapsed.value) {
+      expand();
+    }
   }
 }
 
+// ---- resize handle drag ----
+let resizeStartX = 0;
+let resizeStartWidth = 0;
+
+function startResize(e: MouseEvent) {
+  resizeStartX = e.clientX;
+  resizeStartWidth = sidebarWidth.value;
+  isResizing.value = true;
+  document.addEventListener("mousemove", onResize);
+  document.addEventListener("mouseup", stopResize);
+  document.body.style.cursor = "col-resize";
+  document.body.style.userSelect = "none";
+  e.preventDefault();
+}
+
+function onResize(e: MouseEvent) {
+  if (!isResizing.value) return;
+  const delta = e.clientX - resizeStartX;
+  const newWidth = Math.min(MAX_SIDEBAR_WIDTH, Math.max(MIN_SIDEBAR_WIDTH, resizeStartWidth + delta));
+  sidebarWidth.value = newWidth;
+  lastExpandedWidth.value = newWidth;
+}
+
+function stopResize() {
+  isResizing.value = false;
+  document.removeEventListener("mousemove", onResize);
+  document.removeEventListener("mouseup", stopResize);
+  document.body.style.cursor = "";
+  document.body.style.userSelect = "";
+}
+
 // ---- workspace switcher ----
 const workspaceSwitcherRef = ref<HTMLElement | null>(null);
 const showWorkspaceMenu = ref(false);
@@ -240,6 +299,10 @@ watch(() => props.folderPath, () => {
 
 onBeforeUnmount(() => {
   document.removeEventListener("click", onDocumentClick);
+  document.removeEventListener("mousemove", onResize);
+  document.removeEventListener("mouseup", stopResize);
+  document.body.style.cursor = "";
+  document.body.style.userSelect = "";
 });
 
 // ---- settings modal ----
@@ -259,7 +322,9 @@ function openSettings(page: SettingsPage) {
 
 <template>
   <aside
-      :class="['directory-sidebar flex flex-row transition-all duration-300 ease-in-out overflow-hidden shrink-0', expanded ? 'w-72' : 'w-12']"
+      class="directory-sidebar flex flex-row overflow-hidden shrink-0"
+      :class="{ 'transition-all duration-300 ease-in-out': !isResizing }"
+      :style="{ width: sidebarWidth + 'px' }"
   >
     <!-- ============ Icon bar ============ -->
     <div class="w-12 shrink-0 flex flex-col items-center gap-1 py-3">
@@ -293,7 +358,7 @@ function openSettings(page: SettingsPage) {
     </div>
 
     <!-- ============ Expanded panel ============ -->
-    <div v-show="expanded" class="directory-sidebar-panel flex-1 flex flex-col overflow-hidden">
+    <div v-show="!isCollapsed" class="directory-sidebar-panel flex-1 flex flex-col overflow-hidden">
       <!-- ===== FOLDER VIEW ===== -->
       <div v-if="activeView === 'folder'" class="flex flex-col flex-1 overflow-hidden">
         <!-- File tree -->
@@ -413,6 +478,16 @@ function openSettings(page: SettingsPage) {
         </button>
       </div>
     </div>
+
+    <!-- ============ Resize handle ============ -->
+    <div
+        v-show="!isCollapsed"
+        class="sidebar-resize-handle"
+        :class="{ 'sidebar-resize-handle-active': isResizing }"
+        @mousedown="startResize"
+    >
+      <div class="sidebar-resize-handle-bar"></div>
+    </div>
   </aside>
 
   <SettingsModal
@@ -563,6 +638,7 @@ function openSettings(page: SettingsPage) {
 
 <style scoped>
 .directory-sidebar {
+  position: relative;
   border-right: 1px solid var(--app-border);
   background: color-mix(in srgb, var(--app-sidebar-bg) 82%, transparent);
 }
@@ -571,6 +647,39 @@ function openSettings(page: SettingsPage) {
   border-left: 1px solid var(--app-border);
 }
 
+/* ---- Resize handle ---- */
+.sidebar-resize-handle {
+  position: absolute;
+  top: 0;
+  right: -2px;
+  bottom: 0;
+  z-index: 25;
+  display: flex;
+  width: 7px;
+  align-items: center;
+  justify-content: center;
+  cursor: col-resize;
+  transition: background-color 0.15s ease;
+}
+
+.sidebar-resize-handle:hover,
+.sidebar-resize-handle-active {
+  background: color-mix(in srgb, var(--app-accent) 18%, transparent);
+}
+
+.sidebar-resize-handle-bar {
+  width: 1px;
+  height: 100%;
+  border-radius: 1px;
+  background: transparent;
+  transition: background-color 0.15s ease;
+}
+
+.sidebar-resize-handle:hover .sidebar-resize-handle-bar,
+.sidebar-resize-handle-active .sidebar-resize-handle-bar {
+  background: color-mix(in srgb, var(--app-accent) 36%, transparent);
+}
+
 .sidebar-icon-btn {
   color: var(--app-subtle);
 }
diff --git a/src/components/OutlinePanel.vue b/src/components/OutlinePanel.vue
index 8fb47fb..bf9ebe9 100644
--- a/src/components/OutlinePanel.vue
+++ b/src/components/OutlinePanel.vue
@@ -1,5 +1,5 @@
 <script setup lang="ts">
-import { computed } from "vue";
+import { ref, computed, onBeforeUnmount } from "vue";
 
 const props = defineProps<{
   markdownContent: string;
@@ -42,11 +42,56 @@ const headings = computed<OutlineItem[]>(() => {
 const onHeadingClick = (item: OutlineItem) => {
   emit("headingClick", { text: item.text, level: item.level });
 };
+
+// ---- panel resize ----
+const MIN_PANEL_WIDTH = 150;
+const MAX_PANEL_WIDTH = 500;
+const DEFAULT_PANEL_WIDTH = 208; // w-52
+
+const panelWidth = ref(DEFAULT_PANEL_WIDTH);
+const isResizing = ref(false);
+
+let resizeStartX = 0;
+let resizeStartWidth = 0;
+
+function startResize(e: MouseEvent) {
+  resizeStartX = e.clientX;
+  resizeStartWidth = panelWidth.value;
+  isResizing.value = true;
+  document.addEventListener("mousemove", onResize);
+  document.addEventListener("mouseup", stopResize);
+  document.body.style.cursor = "col-resize";
+  document.body.style.userSelect = "none";
+  e.preventDefault();
+}
+
+function onResize(e: MouseEvent) {
+  if (!isResizing.value) return;
+  const delta = e.clientX - resizeStartX;
+  panelWidth.value = Math.min(MAX_PANEL_WIDTH, Math.max(MIN_PANEL_WIDTH, resizeStartWidth + delta));
+}
+
+function stopResize() {
+  isResizing.value = false;
+  document.removeEventListener("mousemove", onResize);
+  document.removeEventListener("mouseup", stopResize);
+  document.body.style.cursor = "";
+  document.body.style.userSelect = "";
+}
+
+onBeforeUnmount(() => {
+  document.removeEventListener("mousemove", onResize);
+  document.removeEventListener("mouseup", stopResize);
+  document.body.style.cursor = "";
+  document.body.style.userSelect = "";
+});
 </script>
 
 <template>
   <aside
-    class="outline-panel flex flex-col w-52 shrink-0 overflow-hidden"
+    class="outline-panel flex flex-col shrink-0 overflow-hidden"
+    :class="{ 'transition-all duration-300 ease-in-out': !isResizing }"
+    :style="{ width: panelWidth + 'px' }"
   >
     <!-- Header -->
     <div class="outline-panel-header flex items-center px-3 py-3">
@@ -81,15 +126,58 @@ const onHeadingClick = (item: OutlineItem) => {
         </div>
       </template>
     </div>
+
+    <!-- Resize handle -->
+    <div
+      class="outline-resize-handle"
+      :class="{ 'outline-resize-handle-active': isResizing }"
+      @mousedown="startResize"
+    >
+      <div class="outline-resize-handle-bar"></div>
+    </div>
   </aside>
 </template>
 
 <style scoped>
 .outline-panel {
+  position: relative;
   border-right: 1px solid var(--app-border);
   background: color-mix(in srgb, var(--app-sidebar-bg) 82%, transparent);
 }
 
+/* ---- Resize handle ---- */
+.outline-resize-handle {
+  position: absolute;
+  top: 0;
+  right: -2px;
+  bottom: 0;
+  z-index: 25;
+  display: flex;
+  width: 7px;
+  align-items: center;
+  justify-content: center;
+  cursor: col-resize;
+  transition: background-color 0.15s ease;
+}
+
+.outline-resize-handle:hover,
+.outline-resize-handle-active {
+  background: color-mix(in srgb, var(--app-accent) 18%, transparent);
+}
+
+.outline-resize-handle-bar {
+  width: 1px;
+  height: 100%;
+  border-radius: 1px;
+  background: transparent;
+  transition: background-color 0.15s ease;
+}
+
+.outline-resize-handle:hover .outline-resize-handle-bar,
+.outline-resize-handle-active .outline-resize-handle-bar {
+  background: color-mix(in srgb, var(--app-accent) 36%, transparent);
+}
+
 .outline-panel-header {
   border-bottom: 1px solid var(--app-border);
 }