Radiation effect of γ-rays on lignin was studied. The lignin irradiated by γ-rays was characterized by GPC, IR and ,13,C-NMR respectively. It has been shown that cross-link reaction is the key reaction under this experimental condition, while the molecular weight and molecular weight distribution of lignin is increased. IR spectra of irradiated lignin are similar to that of former lignin. The functional groups of irradiated lignin almost have not change compared with former lignin. Hydroxyl groups in irradiated lignin are not only increased but also more stable. It has been found that the main functional groups in the molecular structure of alkali lignin are not destroyed after γ-rays irradiation according to the analysis with,13,C-NMR.