<asp:Button ID="CloseButton" runat="server" Text="Close" OnClientClick="javaScript:window.close(); return false;" />
Or
<input type="button" onclick="JavaScript:window.close();" value="Close"/>
or
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm8.aspx.cs" Inherits="WebApplication17.WebForm8" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title>Untitled Page</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Button" />
</div>
</form>
</body>
</html>
using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
namespace WebApplication17
{
public partial class WebForm8 : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
this.Button1.Attributes.Add("OnClick", "self.close()");
}
protected void Button1_Click(object sender, EventArgs e)
{
Response.Write("<script language='javascript'> { self.close() }</script>");
}
}
}