To obtain a resin composition imparting flexibility to a resin such as a thermoplastic resin, a thermosetting resin and rubber, especially a resin having a functional group such as hydroxy group, carboxy group, amide group or amino group having reactivity with epoxy group without lowering the melt viscosity and affording a molded product with a slight deviation from designed dimensions by a molding method such as an extrusion method, a blow molding method, an injection molding method, a calender forming method or a press forming method.

This resin composition comprises 1-30 pts. mass of a plasticizer composed of a vinyl polymer having epoxy groups, ≤0°C glass transition temperature, 500-30,000 weight-average molecular weight and 0.50-5.00 milliequivalents/g epoxy value and 100 pts. mass of a resin.