 <p>Class level variables can't maintain their value on postback.</p> <p>But there are two ways you can maintain Data on the Page's PostBack: <code>ViewState and Session State</code>. But I would suggest in your Scenario to put it in the <code>ViewState</code>.</p> <pre><code>ViewState["theDataTable"] = theDataTable; Session["theDataTable"] = theDataTable; </code></pre> <p>And then you can access it on the page postback:</p> <pre><code>DataTable theDataTable = (DataTable)ViewState["theDataTable"]; DataTable theDataTable = (DataTable)Session["theDataTable"]; </code></pre>