Objective To investigate the radioprotective effects of genistein (GEN) against radiation-induced DNA damage in human liver cell line L-02．Methods （1）L-02 cells were treated with different concentrations of GEN (1, 5, 10, and 20 μmol/L) for 24 h, and then irradiated with X-ray at the doses of 6, 8, 12,16,and 20 Gy. Forty-eight hours after irradiation, MTT method was applied to examine the proliferation of L-02 cells.（2）L-02 cells were treated with different concentrations of GEN (1, 5, 10, and 20 μmol/L) for 24 h, and then irradiated with X-ray at the doses of 8 Gy (300 cGy/min) . Single cell gel electrophoresis was used to determine the DNA damage after radiation . Results (1)After irradiation with 6, 8 and 12 Gy of X-ray, the cell proliferation rate of 5 μmol/L GEN-pretreated group was significantly increased compared to radiation alone (R) group (P<0.05). But no significant increase was observed in GEN-pretreated groups irradiated with 16 Gy and 20 Gy of X-ray compared with R group. (2)As for the DNA damage, no comet cells were detected in normal control group or all GEN-treated groups without irradiation. After irradiation with 8 Gy of X-ray for 24 h, comet incidences were less than 1% in all GNE-pretreated groups and R group, and comet tail length showed no significant difference between different groups. At 48 h after irradiation, the comet incidence of R group was (24.2±1.2)% and the comet tail length was (283.6±22.3) μm, while both comet incidence and tail length of GEN-pretreated groups were significantly lower than those of R group (P<0.05). The comet incidence and tail length of R group were significantly decreased 72 h after irradiation compared with 48 h after irradiation (P<0.05), and those in 1 μmol/L and 5 μmol/L GEN-pretreated groups were still significantly lower than those of R group (P<0.05), but the comet incidence and tail length of 10 μmol/L and 20 μmol/L GEN-pretreated groups were significantly increased compared to those of R group (P<0.05). Conclusion Low concentration of GEN (1 and 5 μmol/L) can effectively protect the human liver cells L-02 against X-ray (8 Gy)-induced DNA damage.