To set the tab-stops positions in a list box item text, you should send LB_SETTABSTOPS message. To respond to the LB_SETTABSTOPS message, the list box must have been created with the LBS_USETABSTOPS style.
const TabCount=4; var TabStops: array[1..TabCount] of Integer=(10,15,20,30); ... procedure TForm1.FormCreate(Sender: TObject); begin TabListBox1.Perform(LB_SETTABSTOPS,TabCount,LongInt(@TabStops)); end;