Novel polyesteramides were synthesized from p-nitrophenyl, esters of sebacic or adipic acids and diamines containing alpha -amino acid ester groups. The optimal polymerization condition was 60 degreesC in N,N-dimethylformamide. The structures of these polymers were confirmed by IR and NMR. The number-average molecular weights of these polyesteramides ranged from 2280 to 23,600 (except for the polymers containing glycine residues), depending an the nature of the amino acid used. The biodegradability of the polyesteramides was investigated by in vitro hydrolysis with proteases and a Lipase as catalysts in berate buffer solutions. The results indicated that the polymers containing L-phenylalanine were hydrolyzed most effectively by alpha -chymotrypsin, subtilisin Carlsberg, and subtilisin BPN '. The polyesteramides containing other amino acid residues also underwent hydrolysis to different extents, reflecting the substrate specificity of the proteases. Lipase had almost no effect on tile hydrolytic degradation of these polyesteramides. The polymers containing glycine residues were hardly decomposed by any of the the enzymes used.