Hi, Try this code..
its working based on javascript....
Parent page :
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm1.aspx.cs" Inherits="WebApplication1.WebForm1" %>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<script src="jquery.js.js"></script>
<script type="text/javascript">
var openchild = function ()
{
window.open('childpage.aspx', 'popup_window', 'width=300,height=100,left=100,top=100,resizable=yes');
return false;
}
</script>
</head>
<body>
<form id="form1" runat="server">
<table>
<tr>
<td>parent textbox</td>
<td>
<asp:TextBox ID="txtparent" runat="server"></asp:TextBox></td>
</tr>
<tr>
<td colspan="2" align="center">
<asp:Button ID="btnSearch" OnClientClick="return openchild()" runat="server" Text="open child" /></td>
</tr>
</table>
</form>
</body>
</html>
__________________________________________________________________________________________________
child page
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="childpage.aspx.cs" Inherits="WebApplication1.childpage" %>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<script type="text/javascript">
var closechild = function () {
var value = document.getElementById('txtchild').value;
window.opener.document. getElementById('txtparent').value = value;
window.close();
return false;}
</script>
</head>
<body>
<form id="form1" runat="server">
<div>
<table>
<tr>
<td>child textbox</td>
<td>
<asp:TextBox ID="txtchild" runat="server"></asp:TextBox></td>
</tr>
<tr>
<td colspan="2" align="center">
<asp:Button ID="btnclose" OnClientClick="return closechild()" runat="server" Text="close child" /></td>
</tr>
</table>
</div>
</form>
</body>
</html>