diff --git a/extensions/bootstrap/CHANGELOG.md b/extensions/bootstrap/CHANGELOG.md
index 5fced15e10..464c959706 100644
--- a/extensions/bootstrap/CHANGELOG.md
+++ b/extensions/bootstrap/CHANGELOG.md
@@ -12,9 +12,11 @@ Yii Framework 2 bootstrap extension Change Log
 - Enh #1601: Added support for tagName and encodeLabel parameters in ButtonDropdown (omnilight)
 - Enh #1881: Improved `yii\bootstrap\NavBar` with `containerOptions`, `innerContainerOptions` and `renderInnerContainer` (creocoder)
 - Enh #2425: Tabs widget now selects first tab if no active tab is specified (samdark)
+- Enh #2643: Add size attribute to Modal (tof06)
 - Chg #1459: Update Collapse to use bootstrap 3 classes (tonydspaniard)
 - Chg #1820: Update Progress to use bootstrap 3 markup (samdark)
 
+
 2.0.0 alpha, December 1, 2013
 -----------------------------
 
diff --git a/extensions/bootstrap/Modal.php b/extensions/bootstrap/Modal.php
index 276b57c4ae..e498f49233 100644
--- a/extensions/bootstrap/Modal.php
+++ b/extensions/bootstrap/Modal.php
@@ -35,6 +35,10 @@ use yii\helpers\Html;
  */
 class Modal extends Widget
 {
+	const SIZE_LARGE = "modal-lg";
+	const SIZE_SMALL = "modal-sm";
+	const SIZE_DEFAULT = "";
+
 	/**
 	 * @var string the header content in the modal window.
 	 */
@@ -43,6 +47,10 @@ class Modal extends Widget
 	 * @var string the footer content in the modal window.
 	 */
 	public $footer;
+	/**
+	 * @var string the modal size. Can be MODAL_LG or MODAL_SM, or empty for default.
+	 */
+	public $size;
 	/**
 	 * @var array the options for rendering the close button tag.
 	 * The close button is displayed in the header of the modal window. Clicking
@@ -86,7 +94,7 @@ class Modal extends Widget
 
 		echo $this->renderToggleButton() . "\n";
 		echo Html::beginTag('div', $this->options) . "\n";
-		echo Html::beginTag('div', ['class' => 'modal-dialog']) . "\n";
+		echo Html::beginTag('div', ['class' => 'modal-dialog ' . $this->size]) . "\n";
 		echo Html::beginTag('div', ['class' => 'modal-content']) . "\n";
 		echo $this->renderHeader() . "\n";
 		echo $this->renderBodyBegin() . "\n";