PURPOSE: To obtain the title optical disk substrate which can be produced in a short time and has excellent heat resistance by injecting a photoresist composition into a light-transmittable mold, irradiating light and then heating the mold.

CONSTITUTION: The light-transmittable mold to be used has at least a part capable of transmitting light and a glass mold, a heat-resistant plastic mold, a quartz mold, etc., can be exemlified. Light is irradiated on the photoresist composition in the mold to form an injection mold having small birefringence. Then the mold is heated to provide high heat resistance. The light having 20W200W/cm is usually used and irradiated for 10W5min and the heating is usually carried out at 100W250°C. Consequently, an optical disk substrate which can be produced in a short time and has excellent heat resistance and wherein birefringence is hardly generated can be obtained.