A copolymer, poly(L-lactide)-g-poly(N-vinyl pyrrolidone) (PLLA-g-PVP) was prepared with poly(L-lactide) (PLLA) and N-vinyl pyrrolidone in the presence of methanol as a solvent by gamma-ray irradiation. The structure of PLLA-g-PVP was characterized by H-1-NMR and Fourier transform infrared spectroscopy. The PLLA-g-PVP graft ratio calculated by the percentage increase in weight increased with the increase of absorbed dose, and the percentage crystallinity of PLLA-g-PVP decreased with increasing graft ratio. The introduction of the poly(N-vinyl pyrrolidone) chain into PLLA resulted in a decrease in the contact angle of PLLA-g-PVP with increasing graft ratio. In vitro degradation testing showed that PLLA-g-PVP had a higher degradation rate both in the weight-loss test and molecular weight measurement because of a lower crystalline percentage and higher hydrophilicity compared to PLLA. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 3152-3157,2009