Random copolymers of polylactide-co-poly(amino acids) with a molecule weight range of 5,000-20,000 g/mol were obtained by ring-opening polymerization of l-lactic acid O-carboxyanhydride with amino acid-N-carboxyl anhydride in the presence of DMAP as an initiator. The structures of the copolymers were characterized with IR, H-1-NMR, C-13-NMR, and GPC. The results show that the polymerization activity of amino acid-N-carboxyl anhydride is higher than that of l-lactic acid O-carboxyanhydride. Copolymers of polylactide-co-poly(amino acid) can improve the solubility of poly(amino acid) in organic solvents.