 <p>Your Action method is returning a collection of Objects, that would be structured like this;</p> <pre><code>[ { tagName: result1}, {tagName: result2} ... ] </code></pre> <p>Because you use the result directly for the autocomplete, the method needs to return data in one of the <a href="http://jqueryui.com/demos/autocomplete/#remote-jsonp" rel="nofollow">following two formats</a>;</p> <blockquote> <p>The data from local data, a url or a callback can come in two variants:</p> <p>An Array of Strings:<br> <code>[ "Choice1", "Choice2" ]</code></p> <p>An Array of Objects with label and value properties:<br> <code>[ { label: "Choice1", value: "value1" }, ... ]</code></p> </blockquote> <p>Alternatively, you could take the results and map them appropriately to one of the above formats before posting them to the response method.</p>