To obtain a new polymer composition that contains an alternating copolymer of carbon monoxide and an ethylenic unsaturated compound, and has improved impact resistance.

This polymer composition comprises 30-98wt.% of a polymer (A) consisting of repeated units shown by the formula: C(=O)-R (R is a structural unit derived from an ethylenic unsaturated compound), and 70-2wt.% of a block copolymer (B) having a polymer block of a acrylate or methacrylate and a polymer block having a glass transition point of 25°C or below.