diff --git a/components/script/dom/cssstyledeclaration.rs b/components/script/dom/cssstyledeclaration.rs
index df3c492d9da..cacb5afb1a7 100644
--- a/components/script/dom/cssstyledeclaration.rs
+++ b/components/script/dom/cssstyledeclaration.rs
@@ -69,6 +69,7 @@ impl CSSStyleDeclaration {
 
 trait PrivateCSSStyleDeclarationHelpers {
     fn get_declaration(self, property: &Atom) -> Option<PropertyDeclaration>;
+    fn get_important_declaration(self, property: &Atom) -> Option<PropertyDeclaration>;
 }
 
 impl<'a> PrivateCSSStyleDeclarationHelpers for JSRef<'a, CSSStyleDeclaration> {
@@ -77,6 +78,12 @@ impl<'a> PrivateCSSStyleDeclarationHelpers for JSRef<'a, CSSStyleDeclaration> {
         let element: JSRef<Element> = ElementCast::from_ref(*owner);
         element.get_inline_style_declaration(property).map(|decl| decl.clone())
     }
+
+    fn get_important_declaration(self, property: &Atom) -> Option<PropertyDeclaration> {
+        let owner = self.owner.root();
+        let element: JSRef<Element> = ElementCast::from_ref(*owner);
+        element.get_important_inline_style_declaration(property).map(|decl| decl.clone())
+    }
 }
 
 impl<'a> CSSStyleDeclarationMethods for JSRef<'a, CSSStyleDeclaration> {
@@ -144,6 +151,30 @@ impl<'a> CSSStyleDeclarationMethods for JSRef<'a, CSSStyleDeclaration> {
         }
     }
 
+    // http://dev.w3.org/csswg/cssom/#dom-cssstyledeclaration-getpropertypriority
+    fn GetPropertyPriority(self, property: DOMString) -> DOMString {
+        // Step 1
+        let property = Atom::from_slice(property.as_slice().to_ascii_lower().as_slice());
+
+        // Step 2
+        let longhand_properties = longhands_from_shorthand(property.as_slice());
+        if let Some(longhand_properties) = longhand_properties {
+            // Step 2.1 & 2.2 & 2.3
+            if longhand_properties.iter()
+                                  .map(|longhand| self.GetPropertyPriority(longhand.clone()))
+                                  .all(|priority| priority.as_slice() == "important") {
+
+                return "important".to_string();
+            }
+        // Step 3
+        } else if self.get_important_declaration(&property).is_some() {
+            return "important".to_string();
+        }
+
+        // Step 4
+        "".to_string()
+    }
+
     // http://dev.w3.org/csswg/cssom/#dom-cssstyledeclaration-setproperty
     fn SetProperty(self, property: DOMString, value: DOMString,
                    priority: DOMString) -> ErrorResult {
diff --git a/components/script/dom/element.rs b/components/script/dom/element.rs
index 00f481dcd32..b1d85ef8c74 100644
--- a/components/script/dom/element.rs
+++ b/components/script/dom/element.rs
@@ -469,6 +469,7 @@ pub trait ElementHelpers<'a> {
     fn remove_inline_style_property(self, property: DOMString);
     fn update_inline_style(self, property_decl: style::PropertyDeclaration, important: bool);
     fn get_inline_style_declaration(self, property: &Atom) -> Option<style::PropertyDeclaration>;
+    fn get_important_inline_style_declaration(self, property: &Atom) -> Option<style::PropertyDeclaration>;
 }
 
 impl<'a> ElementHelpers<'a> for JSRef<'a, Element> {
@@ -595,6 +596,16 @@ impl<'a> ElementHelpers<'a> for JSRef<'a, Element> {
                         .map(|decl| decl.clone())
         })
     }
+
+    fn get_important_inline_style_declaration(self, property: &Atom) -> Option<style::PropertyDeclaration> {
+        let inline_declarations = self.style_attribute.borrow();
+        inline_declarations.as_ref().and_then(|declarations| {
+            declarations.important
+                        .iter()
+                        .find(|decl| decl.matches(property.as_slice()))
+                        .map(|decl| decl.clone())
+        })
+    }
 }
 
 pub trait AttributeHandlers {
diff --git a/components/script/dom/webidls/CSSStyleDeclaration.webidl b/components/script/dom/webidls/CSSStyleDeclaration.webidl
index 7b0e2213956..38f20af8d4e 100644
--- a/components/script/dom/webidls/CSSStyleDeclaration.webidl
+++ b/components/script/dom/webidls/CSSStyleDeclaration.webidl
@@ -14,7 +14,7 @@ interface CSSStyleDeclaration {
   readonly attribute unsigned long length;
   getter DOMString item(unsigned long index);
   DOMString getPropertyValue(DOMString property);
-  //DOMString getPropertyPriority(DOMString property);
+  DOMString getPropertyPriority(DOMString property);
   [Throws]
   void setProperty(DOMString property, [TreatNullAs=EmptyString] DOMString value,
                                        [TreatNullAs=EmptyString] optional DOMString priority = "");
diff --git a/tests/content/test_getPropertyPriority.html b/tests/content/test_getPropertyPriority.html
new file mode 100644
index 00000000000..85bcde77238
--- /dev/null
+++ b/tests/content/test_getPropertyPriority.html
@@ -0,0 +1,25 @@
+<html>
+  <head>
+    <script src="harness.js"></script>
+  </head>
+  <body>
+    <div id="important" style='outline-color: #111 !important; outline-style: solid !important; outline-width: 1px !important; background-color: #222 !important; color: #FFF'></div>
+    <script>
+      var properties = {
+        'outline-color': 'important',
+        'outline-style': 'important',
+        'outline-width': 'important',
+        'outline': 'important',
+        'background-color': 'important',
+        'background': '',
+        'color': '',
+      };
+      var elem = document.getElementById('important')
+      for (var property in Object.keys(properties)) {
+        var name = Object.keys(properties)[property];
+        var value = properties[name];
+        is(elem.style.getPropertyPriority(name), value, name + ' priority');
+      }
+    </script>
+  </body>
+</html>