Poly(amino acid) has been widely utilized in drug delivery, tissue engineering and biomedical materials. Thebiomateriais based on poly(glutamic acid) are usually modified via copolymerization with other monomers such as L-asparticacid to improve the uncontrolled degradation rate. The ring-opening homo- and co-polymerization of y-benzyl-L-glutamateN-carboxyanhydride (BLG-NCA) and β-benzyl-L-aspartate N-carboxyanhydride (BLA-NCA) were carried out in solution byusing triethylamine (TEA) as initiator. The BLG-NCA homopolymerization could take place even at-30℃ and molecularweight of poly(γ-benzyl-L-glutamate) decreased with increasing polymerization temperature. The BLA-NCA polymerizationdid not occur at -10℃ and was needed to be carried out at 25℃ to improve the polymerization. Poly(γ-benzyl-L-glutamate)and poly(β-benzyl-L-aspartate) with unimodal molecular weigh distribution and weight average molecular weight (Mw) of32100 and 4000 could be obtained at 25℃. The copolymers of γ-benzyl L-glutamate and β-benzyl L-aspartate withunimodal molecular weight distribution and Mw ranging from 5600 to 24600 could be prepared. The useful copolymers ofpoly(L-glutamic acid-co-L-aspartic acid) were further prepared by removal of benzyl groups.