Described are polyamide copolymers having skeletons of a spe­cific structure. The polyamide copolymers have excellent resistance to hydrolysis, low temperature characteristics (low temperature softness), heat aging resistance and mechanical properties as compared to conventional polyamide copolymers. The polyamide copolymers also show excellent processibility and transparency. In particular, polyamide copolymers having a branched structure in the molecule exhibit good properties.