The present invention provides a resin composition capable of forming a film exhibiting a small humidity-dependent variation in optical values; a triazole compound to be incorporated into the resin composition; an optical film and an optical lens, each of which is prepared from the resin composition and exhibits a small humidity-dependent variation in optical values; and a polarizing plate, a circularly polarizing plate, and an image display device, each of which includes the optical film and exhibits excellent moisture resistance. The resin composition of the present invention contains a resin and a compound having a 5-membered or 6-membered aromatic hydrocarbon or heterocyclic ring, wherein the resin is a hygroscopic resin, the compound has at least three specific aromatic rings having a specific NICS value, and the specific aromatic rings are bonded to one another via a single bond or one or two atoms.