PURPOSE: To obtain an optical disk substrate having excellent hardness, light transmittability and solvent resistance by having a hard coat layer consisting of ladder type silicone on at least one face of a synthetic resin substrate.

CONSTITUTION: This optical disk substrate has the hard coat layer consisting of the ladder type silicone on at least one face of the synthetic resin substrate. The useful hard coat material is exemplified by solvent soluble org. polysiloxane partially condensed by the silane expressed by the formula CH3Si(OR)3 or formula C6H5Si(OR)3 or mixture of the silanes adjusted to 1:10W10:1 mixing molar ratio thereof (where R is an alkyl group of 1W6C). The solvents are general org. solvents, for example, alkanol, ketone, ether, alcohol, etc. The preferable film thickness of the had coat layer is 2W10μm. The hardness, light transmittability and solvent resistance are thereby improved and the adhesiveness between the base substrate and the hard coat layer is extremely good.