In an optical recording medium (optical disk recording medium) on which information can be optically written, read and erased by use of a laser light and which comprises a transparent substrate of a synthetic resin and an information-recording layer provided on the surface of the substrate, said synthetic resin consists of an epoxy resin composition comprising an alicyclic epoxy resin or a mixture of an alicyclic epoxy resin and an aromatic epoxy resin; an organic polybasic acid anhydride; a curing accelerator; and an anti-discoloring (anti-oxidizing) agent, the above substrate is a cured product of a cast article of the epoxy resin composition and has a SiO2 or SiO layer or a hard coat layer of a synthetic resin which may have a SiO2 or SiO layer on its surface, whereby the substrate has thermal resistance and abrasion or scratch resistance, and on said layer there is provided an information-recording layer made of a low melting point metal such as Te, Se, Bi or the like or a complex material of said metal and an organic material or a rare earth metal and transition metal series magnetic alloy such as Td-Gd-Fe or the like. Said transparent substrate can easily be obtained by forming a thin film of MgF2, CaF2 or SiC on the inner surface of a casting mold by an ion-plating method, a spattering method or the like in order to facilitate the release of the molded article of the epoxy resin composition from the casting mold, and casting the epoxy resin composition into the mold. The Si2O or SiO layer or the hard coat of synthetic resin is applied on the thus obtained substrate and the information-recording layer is then applied thereto in a conventional manner. The hard coat of synthetic resin can easily be formed by first applying the hard coat layer on the inner surface of the casting mold, then casting the epoxy resin composition into the casting mold and curing the same to transfer the hard coat onto the cured molded article of the epoxy resin composition.