To provide a resin composition that is excellent in heat resistance, dynamic characteristics and toughness in particular and has excellent characteristics for use in an optical film exhibiting negative birefringence, to provide an optical film exhibiting negative birefringence with high toughness that comprises the resin composition and to provide a process for producing the optical film.

The resin composition for the optical film exhibiting negative birefringence comprises 20-85 wt% copolymer (a) having a ratio of an α-olefin residue unit to an N-phenyl-substituted maleimide residue unit of 49:51-35:65 (molar ratio) and a weight average molecular weight of not less than 5×103 to not more than 5×106 and 80-15 wt% acrylonitrile/styrene copolymer (b) having a ratio of an acrylonitrile residue unit to a styrene residue unit of 36:64-50:50 (weight ratio) and a weight average molecular weight of not less than 5×103 to not more than 5×106.