The NMR spectra of polyamide 46/polyamide 6I copolymers, which were obtained by reaction in the molten sate, are studied. Using C-13 NMR, a physical blend of polyamide 46 and polyamide 6I and a polyamide 46/polyamide 6I copolymer could be discriminated. Four kinds of diad sequences are observed in the carbonyl resonance signals of the polyamide 46/polyamide 6I copolymer, and an assignment has been made. From the relative peak areas of the diad sequences and using a statistical method for a four-component polyamide system, the degree of transamidation, the degree of randomness, and the number-average block length have been calculated.