procedure TForm1.RichEdit1MouseDown(Sender: TObject; Button: TMouseButton;

 Shift: TShiftState; X, Y: Integer);

var

 vPoint: TPoint;

begin

 if Button <> mbRight then Exit;

 vPoint := Point(X, Y);

 X := SendMessage(RichEdit1.Handle, EM_CHARFROMPOS,,

    Integer(@vPoint)) and $0000FFFF;// 得到鼠标点击字符位置

 if (X >= RichEdit1.SelStart) and

    (X <= RichEdit1.SelStart + RichEdit1.SelLength) then

    ShowMessage(RichEdit1.SelText);

end;