γ-Benzyl-L-glutamate was synthesized by the reaction of L-glutamate and benzyl alcohol．N-Carboxy-γ-Benzyl-L-glutamate anhydride (NCA) was synthesized from γ-benzyl-L-glutamate and tfiphosgen．MPEG was used to prepare amine-terminated poly(ethylene glycol) monomethyl ether(MPEG-NH2)

which was used to initiate NCA ring opening polymerization and produce poly (ethylene glycol) monomethyl ether/poly(γ-benzyl-L-glutamate) (PMBG) diblock copolymers with various block contents and molecular weights．The structural characteristics of copolymers were attested by means of IR、1H-NMR、DSC and GPC measurements．The results showedthat products of NCA ring opening polymerization initiated by MPEG-NH2 were block copolymers．Their block contents and number-average molecular weights were calculated from 1H-NMR．The hydrophilicity of homopolymer poly(γ-benzyl-L- glutamate was improved by adding hydrophilie MPEG blocks．