The MC3T3-E1 cells were cultured in vitro and treated with different concentrations （0， 1.0， 2.5， 5.0 and 7.5 mmol·L^－1） of nicotine to induce the MC3T3-E1 cell injury； MTT method was used to determine the proliferation activities of cells in various groups and the half inhibitory concentration（IC₅₀）of nicotine was determined.The MC3T3-E1 cells were divided into control group， nicotine group， NAC group and nicotine+different concentrations（2.5，5.0，and 7.5 mmol·L^－1） NAC groups according the IC₅₀ values， and MTT method was used to determine the proliferation activities of cells in various groups； the optimun concentration of NAC was confirmed.The cells were divided into control group，nicotine （4.25 mmol·L^－1） group，NAC（5.0 mmol·L^－1） group and nicotine（4.25 mmol·L^－1） +NAC（5.0 mmol·L^－1） group.The levels of mitochondrial ROS （mitoROS） was assessed with MitoSOX fluorescence staining method； Flow cytometry was used to detect the apoptic rates of MC3T3-E1 cells in various groups； Western blotting method was used to detect the expression level of apoptosis-related proteins B-cell lymphoma-2 （Bcl-2） and Bcl-2 associated X proteins （Bax）in the cells in various groups， and the ratios of Bax/Bcl-2 was calculated.

Compared with 0 mmol·L^－1 nicotine group， the proliferation activities of MC3T3-E1 cells in different concentrations of nicotine groups were significantly decreased （P<0.05） in a dose-dependent manner. The IC₅₀ of nicotine was （4.25±0.03） mmol·L^－1.Compared with control group，the proliferation activity of MC3T3-E1 cells in 4.25 mmol·L^－1 nicotine group was significantly decreased （P<0.05）； compared with nicotine group， the proliferation activites of MC3T3-E1 cells in nicotine+different concentrations of NAC groups were increased（P<0.05）；the proliferation activity of cells in nicotine+5.0 mmol·L^－1 NAC group was the highest. Compared with control group， the levels of mitoROS in the cells in nicotine group was significantly increased （P<0.05）， the apoptotic rate of cells was significantly increased （P<0.05），and the ratio of Bax/Bcl-2 was increased （P<0.05）；compared with nicotine group， the levels of mitoROS in the cells in NAC and nicotine+NAC group were significantly decreased （P<0.05）， the apoptotic rate was significantly reduced （P<0.05），and the ratio of Bax/Bcl-2 in nicotine+NAC group was reduced （P<0.05）.

NAC can alleviate the apoptosis of MC3T3-E1 cells induced by nicotine， and its mechanism may be related to the mitochondrial oxidative stress.