 <p>As specified on MSDN, </p> <blockquote> <p>A multidimensional array is serialized as a one-dimensional array, and you should use it as a flat array.</p> </blockquote> <p>As specified by Phil.Wheeler, this code does what you want:</p> <pre><code>List&lt;int[]&gt; name = new List&lt;int[]&gt;(){ new int[]{ 23, 21, 10 }, new int[]{ 45, 43, 50 }, new int[]{ 23, 21, 90 } }; string ser = (new System.Web.Script.Serialization.JavaScriptSerializer()).Serialize(name); </code></pre> <p>Hope it will help</p>