<asp:GridView ID="dvMergingHeader" runat="server" OnRowCreated="dvMergingHeader_ItemCreated" align="center" AutoGenerateColumns="false"  BorderStyle="None" BorderWidth="1px" CellPadding="4" Width="100%">
	<SelectedRowStyle BackColor="#FFCC66" Font-Bold="True" ForeColor="#663399" />
	 <PagerStyle BackColor="#FFFFCC" ForeColor="#330099" HorizontalAlign="Center" />
               <RowStyle CssClass="ctext" BackColor="LightCyan" Font-Bold="False" VerticalAlign="Top" />
               <HeaderStyle BackColor="gray" Font-Bold="True" CssClass="text" ForeColor="white" Font-Italic="False" Font-Overline="False" Font-Strikeout="False" Font-Underline="False"  HorizontalAlign="Center" VerticalAlign="Middle" />
	
	<asp:BoundField DataField=" Column1"   HeaderText="Column1">
              	 <ItemStyle HorizontalAlign="Left" VerticalAlign="top" />
               </asp:BoundField>
	<asp:BoundField DataField=" Column2"   HeaderText="Column2">
              	 <ItemStyle HorizontalAlign="Left" VerticalAlign="top" />
               </asp:BoundField>
	<asp:BoundField DataField=" Column3"   HeaderText="Column3">
              	 <ItemStyle HorizontalAlign="Left" VerticalAlign="top" />
               </asp:BoundField>
	<asp:BoundField DataField=" Column4"   HeaderText="Column4">
              	 <ItemStyle HorizontalAlign="Left" VerticalAlign="top" />
               </asp:BoundField>
</asp:GridView>

 protected void dvMergingHeader_ItemCreated(object sender, GridViewRowEventArgs e)
    {
        if (e.Row.RowType == DataControlRowType.Header)
        {
            //custom header.
            GridView gvHeader = (GridView)sender;
            GridViewRow gvHeaderRow = new GridViewRow(0, 0, DataControlRowType.Header, DataControlRowState.Insert);
            TableCell tc1 = new TableCell();

            // First Merged column
            tc1.Text = "Merged Column1";
            tc1.ColumnSpan = 2;
            tc1.BackColor = System.Drawing.Color.Brown; 
            
            gvHeaderRow.Cells.Add(tc1l);

             // Second  Merged column
            tc1 = new TableCell();
            tc1.Text = "Merged Column2";
            tc1.ColumnSpan = 2;
            gvHeaderRow.Cells.Add(tc1);

           gvHeader.Controls[0].Controls.AddAt(0, gvHeaderRow);
	
          }
 }