Abstract: Objective To investigate the effects of autophagy on breast cancer cells to tamoxifen resistance.Methods Immunofluorescence was used to count the proportion of the cells with autophagy in MCF-7 and MCF-7/TAMR,as well as,the average of autophagosome in each cells.Western blotting was used to detect the different expressions of p38,c-jun and LC3 in MCF-7 and MCF-7/TAMR.Stepwise selection was used to detect the duration of resistance to different doses of tamoxifen when upregulating or downregulating of LC3.Western blot was facilitated to investigate changes of activity of p38/c-jun.Rusults Compared with MCF-7,the proportion of the cells with autophagosome in MCF-7/TAMR was markedly increased,the same as the average of autophagosome in each cells.Compared with MCF-7,LC3,especially LC3IIprotein expressive levels in MCF-7 / TAMR was significantly increased.The expressive level of LC3 during the induction process of TAM resistance was negative correlated with resistant cell lines.The expressions of phosphorylated p38 and c-Jun in MCF-7/TAMR were significantly increased.Conclusion Autophagy promotes breast cancer cells to resistant to tamoxifen,due to downregulation of the expression of autophagy related proteins which may inhibit the generation of resistant breast cancer cells.This may be a viable treatment strategy for refractory breast cancer.