You can't make that work, RTB doesn't support any kind of user-implemented painting like ListBox.DrawMode. The later versions of the native Windows RichEdit control support justified text, not the one that .NET uses though. You'll need a lot of surgery to make that happen, it starts by
creating a .NET control that uses msftedit.dll. Then you need EM_SETPARAFORMAT to select PARAFORMAT2.wAlignment = PFA_JUSTIFY. Good luck.
Hans Passant.