U can use Query String To Pass value form 1 page to another .
In your First page ->
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Page1.aspx.cs" Inherits="_Default" %>
<!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">
</head>
<body>
<form id="form1" runat="server" >
<asp:DropDownList id="DropDownList1" runat="server" >
<asp:ListItem value="">Select</asp:ListItem>
<asp:ListItem value="1">Hello</asp:ListItem>
<asp:ListItem value="2">World</asp:ListItem>
</asp:DropDownList>
<asp:button id="btnSubmit" onclick="btnSubmit_OnClick" Text="Click Me" Runat="server"></asp:button>
</form>
</body>
</html>
.cs(code behind For 1st page)
protected void btnSubmit_OnClick(object sender, EventArgs e)
{
if (DropDownList1.SelectedItem.Value.Length > 0)
{
Response.Redirect("Page2.aspx?SelectedValue=" + DropDownList1.SelectedValue);
}
}
in second page Create textbox and write following code in code bihind
.cs(2nd page code behind )
protected void Page_Load(object sender, EventArgs e)
{
string v = Request.QueryString["SelectedValue"];
}