Using a polarimetry based on the rotating analyzer ellipsometer, a technique of measuring off-alignment angle between the slow-axis of the LCD (Liquid Crystal Display) polarizing plate and the transmission axis of the compensating plate attached to the polarizing plate is proposed. It is anticipated that this technique will reduce the optic axis off-alignment error coming from the process of attaching the compensating plate to the LCD polarizing plate markedly, and therefore will help maintain the quality of LCD display image uniformly.