Abstract: Objective To evaluate the cytotoxicity of nicotine on L-929 cell and its mechanism in vitro.Methods The growths of L-929 cell stmiulated by nicotine were examined with methyl thiazolyl tetrazo lium(MTT)method.Cell cy cle and apoptosis rates of L-929 cell were measured with flow cytometry(FCM)method.Results Necotine exposure inhib ited the proliferation of L-929 cells at the concentrations of 10 000,1 000,100,10 μg/mL,and 1 μg/mL for 24,48,and 72 hours.Results of relative growth rate(RGR)showed that the cytotoxicity of nicotineat concentrations of 0.01 and 0.1 μg/mL was grade one at 24 and 48 hours.But the cytotoxicity changed to grade two at 72 hours.The cytotoxicity of nic otine at the concentration of 1 0000 μg/mL was grade three at 24 hours,and grade four at 48,72 hours.With the increase of concentration,the cell DNA contents of G₀G₁ phase increased compared with that of normal control group.While those of the G2 and Sgradually declined.Conclusion Nicotine has significant cytotoxicity on L-929 cells and delays the cell cycle of the cells in vitro.