To provide a resin composition capable of forming a cured material such as film, etc., without causing peeling or dissolution, etc., by the influence of heat, and even when the resin composition is used as a fiber-sizing agent, to provide the resin composition capable of forming a molded article having a level without causing the reduction of flexural strength, etc., by the influence of the heat.

This resin composition includes (A) a maleic anhydride-modified vinyl polymer, (B) a compound containing ≥1 kind selected from the group consisting of (b1) a (block)isocyanate and (b2) an amine, and (C) an aqueous medium.