<div>
There must be something else wrong. 
This code using your javascript works perfectly. How are you examining the created &lt;option&gt;'s? 

<pre><code class="code-10 nolinks" id="code-20-41790079-1">&lt;!doctype html&gt;
&lt;html&gt;
&lt;head&gt;
&lt;script src=&quot;http://code.jquery.com/jquery.js&quot;&gt;&lt;/script&gt;
&lt;/head&gt;
&lt;body&gt;
&lt;select id=&quot;test&quot;&gt;&lt;/select&gt;
&lt;script&gt;
function OnSuccess(response) {
 var sc = $('#test').empty();
 $.each(response.d, function (i, d) {
 sc.append($('&lt;option/&gt;').val(d).html(d)); 
 });
}
var data = {
 d: [
 'test1',
 'test2',
 'test3'
 ]
}
OnSuccess(data);
&lt;/script&gt;
&lt;/body&gt;
&lt;/html&gt;
</code></pre>
 
Working sample <a href="http://www.marcorpsa.com/ee/t1560.html" rel="ugc">here</a>
</div>

<div>
try this one : 
 

<pre><code class="code-10 nolinks" id="code-20-41792053-1">function OnSuccess(response) {

 var productSubCode = '#' + '&lt;%=PRODUCT_SUBCODE.ClientID %&gt;';
 var sc = $(productSubCode).empty();
 var jsonString = response.d;
 var jsonObject = $.parseJSON(jsonString);
 $.each(jsonObj, function (i, d) {
 sc.append($('&lt;option/&gt;').val(d).html(d)); 
 });
 //alert(&quot;Success: &quot; + response.d);
 }
</code></pre>
 
optimized(?) version : 

<pre><code class="code-10 nolinks" id="code-20-41792053-2">function OnSuccess(response) {

 var productSubCode = '#' + '&lt;%=PRODUCT_SUBCODE.ClientID %&gt;';
 var jsonString = response.d;
 var jsonObject = $.parseJSON(jsonString); // please note $.parseJSON is deprecated since jquery 3.0
 var sc = new Array();
 for(var i=0;i&lt;jsonObject.length;i++)
 {
 var d = jsonObject[i];
 sc.push(&quot;&lt;option value='&quot; + d +&quot;'&gt; + d + &quot;&lt;/option&gt;&quot;); 
 };
 $(productSubCode).html(sc.join(&quot;&quot;));
 //alert(&quot;Success: &quot; + response.d);
 }
</code></pre>
</div>

<div>
The accepted answer ask questions when my last answer solve the issue especially my optimised version. 
We know .Net return : {d:&quot;the json string&quot;}
</div>

<div>
<div class="content wysiwyg-content">
<pre><code class="code-1 nolinks" id="code-10-28968588-1">function OnSuccess(response) {

 var productSubCode = '#' + '&lt;%=PRODUCT_SUBCODE.ClientID %&gt;';
 var sc = $(productSubCode).empty();
 $.each(response.d, function (i, d) {
 sc.append($('&lt;option/&gt;').val(d).html(d)); 
 });
 //alert(&quot;Success: &quot; + response.d);
 }
</code></pre>
 
It seems like OnSuccess return me &nbsp;&lt;select&gt;&lt;option&gt;Test&lt;/option&gt;&lt;/select&gt; only. 
How can I get a point return me below: 
 
&lt;select&gt;&lt;option value=&quot;Test&quot;&gt;Test&lt;/option&gt;&lt;/select&gt;
</div>
</div>

(CODE)

It seems like OnSuccess return me <select><option>Test</option></select> only.
How can I get a point return me below:

<select><option value="Test">Test</option></select>

jquery, dropdown

jQuery (Core) is a cross-browser JavaScript library that provides abstractions for common client-side tasks such as Document Object Model (DOM) traversal, DOM manipulation, event handling, animation and Ajax. jQuery also provides a platform to create plugins that extend jQuery's capabilities beyond those already provided by the library.

jQuery

JavaScript is a dynamic, object-based language commonly used for client-side scripting in web browsers. Recently, server side JavaScript frameworks have also emerged. JavaScript runs on nearly every operating system and  in almost every mainstream web browser.

JavaScript

Asynchronous JavaScript and XML (AJAX) is a group of interrelated Web development techniques used on the client-side to create asynchronous Web applications. With AJAX, web applications can send data to and retrieve from a server asynchronously (in the background) without interfering with the display and behavior of the existing page. HTML and CSS can be used in combination to mark up and style information. The Document Object Model (DOM) is accessed with JavaScript to dynamically display and allow interaction with the information presented.