diff --git a/src/reader.rs b/src/reader.rs
index a9c4176..9c6b3ad 100644
--- a/src/reader.rs
+++ b/src/reader.rs
@@ -62,7 +62,9 @@ pub fn reading_view(
     let has_bookmark = bookmarks.iter().any(|b| b.section == *current_section && b.page == *current_page);
 
     // --- Sidebar (TOC + Bookmarks) ---
-    let mut sidebar_tab: usize = 0;
+    let sidebar_tab_id = ui.make_persistent_id("sidebar_tab");
+    let mut sidebar_tab: usize = ui.data_mut(|d| *d.get_temp_mut_or_default::<usize>(sidebar_tab_id));
+
     if *sidebar_open {
         egui::SidePanel::left("toc_sidebar")
             .resizable(true)
@@ -73,8 +75,14 @@ pub fn reading_view(
                     let bm_response = ui.selectable_label(sidebar_tab == 1,
                         format!("🔖 书签 ({})", bookmarks.len())
                     );
-                    if toc_response.clicked() { sidebar_tab = 0; }
-                    if bm_response.clicked() { sidebar_tab = 1; }
+                    if toc_response.clicked() {
+                        sidebar_tab = 0;
+                        ui.data_mut(|d| *d.get_temp_mut_or_default::<usize>(sidebar_tab_id) = 0);
+                    }
+                    if bm_response.clicked() {
+                        sidebar_tab = 1;
+                        ui.data_mut(|d| *d.get_temp_mut_or_default::<usize>(sidebar_tab_id) = 1);
+                    }
                 });
                 ui.separator();
                 if sidebar_tab == 0 {