An apparatus for manufacturing a printed light guide plate includes a working platform (23), and a heater (24) coupled to the working platform. A transparent slab (21) is disposed on the working platform. The purpose of coupling the heater to the working platform is to maintain the transparent slab a constant temperature in the range from about 40.degree. C. to about 45.degree. C., such that as few water molecules as possible are absorbed into the transparent slab. The quality of the manufactured printed light guide plate is thus improved.