Abstract: Objective To observe the effectof environmental estrogenic chemicals(EECs)octylphenol and genistein on DNA damage and proliferation of MDA-MB-231 breastcancer cells.Methods MDA-MB-231 breastcancer cell were cultured with 2,8 and 32μmol/L octylphenol or genistein on 24,48 or 72 h.The proliferation and DNA damage of MDA-MB-231 breastcancer cell were observed by M TT testand single cell gel electrophoresis assay.Results Octylphenol could inhibit the proliferation of MDA-MB-231 cell and increase the DNA damage of breastcancer cells significantly and show doseresponse and time-response.2 and 8μmol/L genistein could promote the proliferation of MDA-MB-231 cell,butthe DNA damage did notchange significantly.32μmol/L genistein could inhibitthe proliferation of MDA-MB-231 cell and increase comettail length of breastcancer significantly.The comettail length(CTL)in genisteintreated group was notas long as thatin octylphenlo-treated group.Conclusion Octylphenol and high-concentration of genistein can induce DNA damage and inhibitthe proliferation of MDA-MB-231 breastcancer cells,butDNA damage in genistein-treated group is notas serious as that in octylphenoltreated group.