Abstract: Objective To investigate the effects of cadmium on the growth of MCF-7 breast cancer cells and estrogen receptor expression.Methods Methyl thiazolyl tetrazolium(MTT) assay was used to estimate the best time and dose of cadmium to promote the proliferation of MCF-7 cells.The death of cells was measured via flow cytometry.The ability of cell migration was evaluated with wound healing assay.The protein expression of estrogen receptor was detected by western blot.The changes of cell proliferation and estrogen receptors expression while estrogen receptors were blocked by estrogen receptor antagonist were observed.Results The effect of cadmium exposure on MCF-7 cell proliferation promotion was most significant for the cadmium treatment of 1 μmol/L for 24 hours and 1 nmol/L for 72 hours,with the proliferation rate of 133.0% and 138.0%.Cadmium exposure of 1 nmol/L for 72 hours could significantly inhibit the death of MCF-7 cells,with a lower proportion of dead cell(28.5%) compared to that of the control group(44.5%)(t=4.557,P<0.05);the cell migration ability was enhanced;the scratch wound healing rate was 25.7%,with a significant difference compared with that of the control group;the estrogen receptor α protein expression was increased.The estrogen receptor antagonist could suppress the effect of cadmium treatment on proliferation of MCF-7 cells and antagonize the increase of estrogen receptor α protein expression.Conclusion Long-time low-dose cadmium treatment can promote the proliferation of MCF-7 breast cancer cells and the effect maybe relate to the activation of estrogen receptor α.