Method-1
<div>
<table>
<tr>
<td><asp:GridView ID="GridView1" runat="server"></asp:GridView></td>
<td><asp:GridView ID="GridView2" runat="server"></asp:GridView></td>
</tr>
</table>
</div>
Method-2
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm7.aspx.cs" Inherits="WebApplication16.WebForm7" %>
<!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>
<style type="text/css">
#leftPanel
{
width:300px;
float:left;
position:relative;
}
#rightPanel
{
width:300px;
float:left;
position:relative;
}
</style>
</head>
<body>
<form id="form1" runat="server">
<div id="leftPanel">
<asp:GridView ID="GridView1" runat="server">
</asp:GridView>
</div>
<div id="rightPanel">
<asp:GridView ID="GridView2" runat="server">
</asp:GridView>
</div>
</form>
</body>
</html>