The invention is a resin composition containing following polymer (A) and polymer (B), wherein a content of the polymer (A) is 1 to 80 wt % based on the total weight of the polymer (A) and the polymer (B), polymer (A) is a alicyclic structure-containing hydrogenated polymer having a heat distortion temperature of 170° C. or higher, polymer (B) is a polymer incompatible with the polymer (A) and having a heat distortion temperature of lower than 170° C., a microporous film formed by using the resin composition, a separator including the microporous film, and a secondary battery having the separator. One aspect of the invention provides a resin composition suitably used as a raw material for a separator of a secondary battery excellent in safety, a microporous film obtained by forming the resin composition, a separator including the microporous film, and a secondary battery having the separator.