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A novel pH-and thermo-responsive block copolymer based on polypeptide was synthesized by ring-opening polymerization of γ-benzyl-L-glutamate-N-carboxyanhydride(BLG-NCA)with PEG-diamine as a macroinitiator and followed by aminolysis reaction.The resulting biodegradable and biocompatible tri-block copolymer,poly[2-(dibutylamino)ethyl-L-glutamate]-poly(ethylene glycol)-block-poly[2-(dibutylamino)ethyl-L-glutamate](PNLG-b-PEG-b-PNLG),showed a low viscosity sol state at low pH(pH-6.4)or at low temperature(250C)but it formed good gel at physiological condition(pH-7.4 and 370C).The gelation behaviors could be control by changing the ratio between hydrophobic moiety and pH-sensitive moiety.The structure of the PNLG-b-PEG-b-PNLG copolymer was confirmed by H-NMR and gel permeation chromatography(GPC).However the hydrogel solution(30wt%and pH-6.4)formed strong gel instantly without major inflammation when it injected subcutaneously into the Sprague–Dawley(SD)rats.The PNLG-b-PEG-b-PNLG copolymer did not show any cytotoxicity in vitro.So PNLG-b-PEG-b-PNLG is a potential candidate for drug and gene delivery.