An optical test system includes a stage region to accommodate an object to be tested, a first incident optical system which changes a first polarization state of a first light beam to a second polarization state and provide the first light beam in the second polarization state to the stage region in a first direction at a first incident angle which is not a right angle, a second incident optical system which changes a third polarization state of a second light beam to a fourth polarization state and inputs the second light beam in the fourth polarization state to the stage region in a second direction at a second incident angle which is not a right angle, and a main optical system to detect a first reflected light beam reflected from the stage region at a first reflection angle different from the first and second incident.