<script type="text/javascript">function OpenPopup() { window.open("popup.aspx","List","scrollbars=no,resizable=no,width=400,height=280"); return false;}</script><asp:TextBox ID="txtPopupValue" runat="server" Width="327px"></asp:TextBox><asp:Button ID="Button1" runat="server" Text="Show List" />

<script language="javascript">function GetRowValue(val){ // hardcoded value used to minimize the code. // ControlID can instead be passed as query string to the popup window window.opener.document.getElementById("ctl00_ContentPlaceHolder1_TextBox2").value = val; window.close();}</script><asp:GridView ID="GridView1" runat="server" DataSourceID="SqlDataSource1"> <Columns> <asp:TemplateField> <AlternatingItemTemplate> <asp:Button ID="btnSelect" runat="server" Text="Select" /> </AlternatingItemTemplate> <ItemTemplate> <asp:Button ID="btnSelect" runat="server" Text="Select" /> </ItemTemplate> </asp:TemplateField> </Columns></asp:GridView>

protected void GridView1_RowDataBound(object sender, System.Web.UI.WebControls.GridViewRowEventArgs e) { if ((e.Row.RowType == DataControlRowType.DataRow)) { //assuming that the required value column is the second column in gridview ((Button)e.Row.FindControl("btnSelect")).Attributes.Add("onclick", "javascript:GetRowValue('" + e.Row.Cells[1].Text + "')"); } }