To obtain the subject film with excellent optical properties, heat resistance, mechanical properties and surface smoothness by using a composition comprising a maleimide-olefin-based copolymer and a copolymer of specific composition.

This film with a thickness of pref. 10-500 μm is obtained by using a resin composition comprising (A) 1-99 wt.% of a maleimide-olefin copolymer with a number-average molecular weight of 1×103 to 5×106 composed of 40-60 mol% of constituent of formula I (R1 is H or a 1-6C alkyl) and 60-40 mol% of constituent of formula II (R2 and R3 are each H or a 1-6C alkyl) and (B) 99-1 wt.% of an acrylonitrile-styrene copolymer containing 21-45 wt.% of acrylonitrile unit.