A process for producing an episulfide compound for an optical material of the present invention includes a step of chlorinating glycerin to obtain dichloropropanol; a step of epoxidizing the dichloropropanol to obtain epichlorohydrin; a step of reacting the epichlorohydrin with a sulfating agent to obtain a bis(chlorohydrin) (di)sulfide compound thought a thiol compound; a step of epoxidizing the bis(chlorohydrin) (di)sulfide compound under basic conditions to obtain an epoxy compound; and a step of reacting the epoxy compound with a sulfating agent to obtain an episulfide compound represented by following General Formula (1):

##STR00001## wherein, in the formula, n represents 0 or 1.

A photocurable composition including a base generator, a polyiso(thio)cyanate compound, and a polythiol compound, in which the base generator includes at least one selected from the group consisting of compounds represented by Formula (1) to Formula (4). In Formulae (1), (3) and (4), each of R.sub.1 to R.sub.4 independently represents a substituent. In Formula (2), each of R.sub.1 to R.sub.7 independently represents an alkyl group having from 1 to 8 carbon atoms or a cycloalkyl group having from 3 to 8 carbon atoms, and R.sub.8 to R.sub.11 respectively have the same meanings as in R.sub.5 to R.sub.8 in Formula (1). In Formula (3), n represents an integer from 1 to 3.

##STR00001##

An episulfide compound and an optical material composition thereof are provided. The episulfide compound possesses a sulfoxide structure, and the presence of the polar group can effectively improve the alkali corrosion resistance of optical material substrates and reduce the rate of substrate burn, thereby improving substrate yield and reducing production costs.