How Can i disable first item of my dropdown list in ASP.NET?

While you are reading items from dropdown, you add below condition, this way option
--Select-- never gets executed.

if (ddl.SelectedIndex != 0) // ddl being your dropdown
{
   // add your code here.   
}

OR

You can disable the button if selected index of your dropdown is zero (0).
This is assuming that you have a button click event which uses dropdown value.

Use jquery for Disabling the dropdown list items like below

$(document).ready(function() {   
   $('#ddlListId option:contains("HTML")').attr("disabled","disabled");
});​

Hope this helps

hi please check my ans

<asp:DropDownList runat="server" ID="ddlBank">
  <asp:ListItem Text="Select" Value="" disabled="disabled" />
  <asp:ListItem Text="bank 1 " Value="bank 1"  />
  <asp:ListItem Text="bank 2 " Value="bank 2"  />
  <asp:ListItem Text="bank 3 " Value="bank 3"  />
  <asp:ListItem Text="Restaurant" Value="Restaurant" disabled="disabled" />
  <asp:ListItem Text="Test" Value="value"  />
  <asp:ListItem Text="restaurant 1" Value="restaurant 1"  />
  <asp:ListItem Text="restaurant 2" Value="restaurant 2" />
  <asp:ListItem Text="restaurant 3" Value="restaurant 3"  />

Use C#:

ddlListId.Items.FindByValue("Item1").Attributes.Add("Disabled", "Disabled");