A resin product wherein a resin B has pillar structures or lamellar structures inside a resin A is molded by kneading the resin A and the resin B that serves as a base material in an injection molding machine while heating both of the resins to at least a temperature at which both of the resins are melted at least partially. The resin product is soaked in a solution having higher erosion capability with respect to the resin A than the resin B, thereby dissolving the resin B and forming an uneven structure on the surface. As a result, an uneven structure having various shapes, densities or depths which are precisely adjustable can be formed at low cost. And provided are a resin structure and a production method thereof that can maintain wettability control or optical property control of the molded article over a long period of time.