The invention provides a light guide plate jig used for placing a light guide plate. The light guide plate jig comprises a tray which comprises a case and a plurality of supporting pieces contained in the case. A gap between the adjacent supporting pieces forms a sliding rail. The light guide plate jig further comprises a sliding piece used for supporting the light guide plate. The sliding piece can move along the slide rail. As the sliding piece can move along the sliding rail, according to dimension difference of the light guide plate, the number of the sliding piece used for supporting the light guide plate and the distance between sliding pieces can be adjusted, and therefore the light guide plate can be prevented from being deformed due to uneven stress.