According to the present invention, a composition for optical material, which is capable of providing a homogeneous optical material, can be prepared through pre-polymerization reaction between (a) an inorganic compound having a sulfur atom and (b) an episulfide compound using a hindered amine as a catalyst, followed by mixing with (c) a polythiol compound and (d) a polyisocyanate compound. Moreover, this composition for optical material can be polymerized and cured to thereby provide an optical material having high refractive index (ne of 1.73 or higher), high strength (an elongation of 13% or more in three-point bend test and good drilling resistance), and high heat resistance (a softening point of 70° C. or higher, as measured by TMA).