Poly (L-lactic acid) grafting with N-vinylpyrrolidone (PLLA-g-PVP) was prepared by radiation in the presence of methanol as a solvent. The effect of absorbed dose on grafting ratio was investigated and the structures of PLLA-g-PVP were characterized by ,1,H-NMR, FT-IR and DSC. It shows that grafting ratio increases with increment of absorbed dose and grafting ratio reach 14.9 % at the absorbed dose of 5 kGy. The peaks of C=O stretching in chain of NVP occur in 1660~1671 cm,-1, which shift to higher wave numbers increasing with absorbed dose. In ,1,H-NMR, the area ratio of methyl to methine is more than 3:1 which indicates the position of grafting reaction may locate in methine attaching to methyl of PLLA. Enthalpy of PLLA increases with increment of absorbed dose, and Enthalpy of PLLA-g-PVP decreases with increment of absorbed dose.