Design html Code:
<asp: dropdownlist id="DropDownList1" runat="server">
<asp: listitem Red</asp:listitem>
<asp:listitem<Green</asp:listitem>
<asp: dropdownlist>
protected void Page_Load(object sender, EventArgs e)
{
SetTooltip(DropDownList1);
}
public static void SetTooltip(ListControl lc)
{
for (int i = 0; i < lc.Items.Count; i++)
{
lc.Items[i].Attributes.Add("title", lc.Items[i].Text);
}
}