To obtain the subject copolymer having high glass transition temperature and free from problems of poor fluidity and insufficient mechanical properties, etc., by copolymerizing a specific polyamide unit with an N-substituted maleimide unit.

This polyamide copolymer is composed of 60-99.5 pts.wt. of a polyamide unit of formula I (R1 is a 4-18C aliphatic group) and/or formula II (R2 and R3 are each a 4-18C aliphatic group or aromatic group) and 0.5-40 pts.wt. of an N-substituted maleimide unit of formula III (R4 is H or a 1-18C aliphatic or aromatic group). The unit I is preferably derived from aminocaproic acid, caprolactam, etc., and the unit III is preferably derived from N- phenylmaleimide or N-cyclohexylmaleimide. The objective copolymer can be produced by reacting a polyamide composed of the unit I and/or II with an N-substituted maleimide and/or poly(N-substituted maleimide) having terminal carboxyl group at 150-300°C preferably in an inert atmosphere.