I have a collection which is name Users.Table seems like

Users

ID Name

1 John 2 Steve 3 Steve 4 Mike

I m binding this collection into dropdownlist.When I set LLBLGenProDataSource 's AllowDuplicate property False nothing happen.But I want distinct data. What can I do ? And Is it possible to write code manually for distinct?

There is no dupliactes in the table you have posted. AllowDuplicate (false) / Distinct is performed on th eentire row, not on a single column.