The present invention inhibits the clouding of cured products obtained by polymerizing and curing a composition including sulfur and an episulfide compound, and inhibits clouding particularly in lenses, called plus-power lenses, that have large central thicknesses; and provides a composition for optical materials with which it is possible to predict and assess whether or not clouding will occur after curing and to determine quality at a stage before polymerization and curing. These objectives are achieved by, for example, a composition for optical materials that includes: sulfur, the turbidity value of which when made into a 30-mass % carbon disulfide solution is 10 ppm or less; and an episulfide compound. That is, clouding is prevented and excellent transparency is achieved in optical materials produced from said composition for optical materials that comprises an episulfide compound and sulfur that satisfies the aforementioned condition in terms of turbidity value.