diff --git a/app/build.gradle b/app/build.gradle
index 8817da0..f29092c 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -69,4 +69,5 @@ dependencies {
     compile 'com.android.support:support-v13:24.1.0'
     compile project(':img-selector')
     compile 'com.facebook.stetho:stetho:1.4.1'
+    compile 'com.github.houxg:FlexLayout:1.2'
 }
diff --git a/app/src/main/java/org/houxg/leanotelite/editor/Editor.java b/app/src/main/java/org/houxg/leanotelite/editor/Editor.java
index 50bcb6b..14ef1ca 100644
--- a/app/src/main/java/org/houxg/leanotelite/editor/Editor.java
+++ b/app/src/main/java/org/houxg/leanotelite/editor/Editor.java
@@ -45,6 +45,10 @@ public abstract class Editor {
 
     public abstract void updateLink(String title, String url);
 
+    public abstract void redo();
+
+    public abstract void undo();
+
     public abstract void toggleOrderList();
 
     public abstract void toggleUnorderList();
diff --git a/app/src/main/java/org/houxg/leanotelite/editor/MarkdownEditor.java b/app/src/main/java/org/houxg/leanotelite/editor/MarkdownEditor.java
index 58422d7..df4086c 100644
--- a/app/src/main/java/org/houxg/leanotelite/editor/MarkdownEditor.java
+++ b/app/src/main/java/org/houxg/leanotelite/editor/MarkdownEditor.java
@@ -86,6 +86,16 @@ public class MarkdownEditor extends Editor {
         execJs(String.format(Locale.US, "ZSSEditor.updateLink('%s', '%s');", url, title));
     }
 
+    @Override
+    public void redo() {
+        execJs("MD.undoMgr.redo()");
+    }
+
+    @Override
+    public void undo() {
+        execJs("MD.undoMgr.undo()");
+    }
+
     @Override
     public void toggleOrderList() {
         execJs("ZSSEditor.setOrderedList();");
diff --git a/app/src/main/java/org/houxg/leanotelite/editor/RichTextEditor.java b/app/src/main/java/org/houxg/leanotelite/editor/RichTextEditor.java
index ba4ee80..9b178a5 100644
--- a/app/src/main/java/org/houxg/leanotelite/editor/RichTextEditor.java
+++ b/app/src/main/java/org/houxg/leanotelite/editor/RichTextEditor.java
@@ -2,6 +2,7 @@ package org.houxg.leanotelite.editor;
 
 
 import android.annotation.SuppressLint;
+import android.text.TextUtils;
 import android.util.Log;
 import android.webkit.WebChromeClient;
 import android.webkit.WebView;
@@ -95,6 +96,16 @@ public class RichTextEditor extends Editor implements OnJsEditorStateChangedList
         execJs(String.format(Locale.US, "ZSSEditor.updateLink('%s', '%s');", url, title));
     }
 
+    @Override
+    public void redo() {
+        execJs("ZSSEditor.redo();");
+    }
+
+    @Override
+    public void undo() {
+        execJs("ZSSEditor.undo();");
+    }
+
     @Override
     public void toggleOrderList() {
         execJs("ZSSEditor.setOrderedList();");
diff --git a/app/src/main/java/org/houxg/leanotelite/ui/edit/EditorFragment.java b/app/src/main/java/org/houxg/leanotelite/ui/edit/EditorFragment.java
index a81edee..ce565d4 100644
--- a/app/src/main/java/org/houxg/leanotelite/ui/edit/EditorFragment.java
+++ b/app/src/main/java/org/houxg/leanotelite/ui/edit/EditorFragment.java
@@ -44,7 +44,7 @@ public class EditorFragment extends Fragment implements Editor.EditorListener {
     private EditorFragmentListener mListener;
     private Editor mEditor;
 
-    @BindView(R.id.ll_tools)
+    @BindView(R.id.fl_tools)
     View mToolContainer;
 
     @BindView(R.id.btn_bold)
@@ -201,6 +201,16 @@ public class EditorFragment extends Fragment implements Editor.EditorListener {
         mEditor.toggleItalic();
     }
 
+    @OnClick(R.id.btn_undo)
+    void undo() {
+        mEditor.undo();
+    }
+
+    @OnClick(R.id.btn_redo)
+    void redo() {
+        mEditor.redo();
+    }
+
     public void setEditingEnabled(boolean enabled) {
         mIsEditingEnabled = enabled;
         mEditor.setEditingEnabled(enabled);
diff --git a/app/src/main/res/drawable-xxhdpi/ic_insert_link_black_disable.png b/app/src/main/res/drawable-xxhdpi/ic_insert_link_black_disable.png
index e2858fa..3e411ad 100644
Binary files a/app/src/main/res/drawable-xxhdpi/ic_insert_link_black_disable.png and b/app/src/main/res/drawable-xxhdpi/ic_insert_link_black_disable.png differ
diff --git a/app/src/main/res/drawable-xxhdpi/ic_insert_link_black_enable.png b/app/src/main/res/drawable-xxhdpi/ic_insert_link_black_enable.png
new file mode 100644
index 0000000..6454bde
Binary files /dev/null and b/app/src/main/res/drawable-xxhdpi/ic_insert_link_black_enable.png differ
diff --git a/app/src/main/res/drawable-xxhdpi/ic_redo_black_disable.png b/app/src/main/res/drawable-xxhdpi/ic_redo_black_disable.png
new file mode 100644
index 0000000..1c55e8d
Binary files /dev/null and b/app/src/main/res/drawable-xxhdpi/ic_redo_black_disable.png differ
diff --git a/app/src/main/res/drawable-xxhdpi/ic_redo_black_enable.png b/app/src/main/res/drawable-xxhdpi/ic_redo_black_enable.png
new file mode 100644
index 0000000..f83453f
Binary files /dev/null and b/app/src/main/res/drawable-xxhdpi/ic_redo_black_enable.png differ
diff --git a/app/src/main/res/drawable-xxhdpi/ic_undo_black_disable.png b/app/src/main/res/drawable-xxhdpi/ic_undo_black_disable.png
new file mode 100644
index 0000000..bfcacc4
Binary files /dev/null and b/app/src/main/res/drawable-xxhdpi/ic_undo_black_disable.png differ
diff --git a/app/src/main/res/drawable-xxhdpi/ic_undo_black_enable.png b/app/src/main/res/drawable-xxhdpi/ic_undo_black_enable.png
new file mode 100644
index 0000000..ea63c38
Binary files /dev/null and b/app/src/main/res/drawable-xxhdpi/ic_undo_black_enable.png differ
diff --git a/app/src/main/res/layout/fragment_editor.xml b/app/src/main/res/layout/fragment_editor.xml
index 18023b1..5327c38 100755
--- a/app/src/main/res/layout/fragment_editor.xml
+++ b/app/src/main/res/layout/fragment_editor.xml
@@ -4,11 +4,12 @@
     android:layout_height="match_parent"
     android:orientation="vertical">
 
-    <LinearLayout
-        android:id="@+id/ll_tools"
+    <org.houxg.flexlayout.FlexLayout
+        android:id="@+id/fl_tools"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:layout_alignParentBottom="true"
+        app:justify_content="space_between"
         android:background="#EEEEEE">
 
         <ImageView
@@ -16,49 +17,49 @@
             style="@style/FormatButton"
             android:src="@drawable/ic_insert_photo_black_disable" />
 
-        <include layout="@layout/separator_horizontal" />
-
         <org.houxg.leanotelite.widget.ToggleImageButton
             android:id="@+id/btn_link"
             style="@style/FormatButton"
             android:src="@drawable/ic_insert_link_black_disable" />
 
-        <include layout="@layout/separator_horizontal" />
-
         <org.houxg.leanotelite.widget.ToggleImageButton
             android:id="@+id/btn_order_list"
             style="@style/FormatButton"
             app:checkedDrawable="@drawable/ic_format_list_bulleted_black_enable"
             app:uncheckedDrawable="@drawable/ic_format_list_bulleted_black_disable" />
 
-        <include layout="@layout/separator_horizontal" />
-
         <org.houxg.leanotelite.widget.ToggleImageButton
             android:id="@+id/btn_unorder_list"
             style="@style/FormatButton"
             app:checkedDrawable="@drawable/ic_format_list_numbered_black_enable"
             app:uncheckedDrawable="@drawable/ic_format_list_numbered_black_disable" />
 
-        <include layout="@layout/separator_horizontal" />
-
         <org.houxg.leanotelite.widget.ToggleImageButton
             android:id="@+id/btn_bold"
             style="@style/FormatButton"
             app:checkedDrawable="@drawable/ic_format_bold_black_enable"
             app:uncheckedDrawable="@drawable/ic_format_bold_black_disable" />
 
-        <include layout="@layout/separator_horizontal" />
-
         <org.houxg.leanotelite.widget.ToggleImageButton
             android:id="@+id/btn_italic"
             style="@style/FormatButton"
             app:checkedDrawable="@drawable/ic_format_italic_black_enable"
             app:uncheckedDrawable="@drawable/ic_format_italic_black_disable" />
-    </LinearLayout>
+
+        <ImageView
+            android:id="@+id/btn_undo"
+            style="@style/FormatButton"
+            android:src="@drawable/ic_undo_black_disable" />
+
+        <ImageView
+            android:id="@+id/btn_redo"
+            style="@style/FormatButton"
+            android:src="@drawable/ic_redo_black_disable" />
+    </org.houxg.flexlayout.FlexLayout>
 
     <org.houxg.leanotelite.widget.LeaWebView
         android:id="@+id/web_editor"
         android:layout_width="match_parent"
         android:layout_height="match_parent"
-        android:layout_above="@id/ll_tools" />
+        android:layout_above="@id/fl_tools" />
 </RelativeLayout>