Abstract: Objective To investigate the effect of β-ionone on cell apoptosis induction in Michigan Cancer Foundation-7(MCF-7)human mammary cancer cells positive to estrogens(Er⁺).Methods The MCF-7 cells were treated with various concentrations(25,50,100,and 200 μmol/L)of β-ionone and a negative control group was set.The growth curve of the cells was calculated;the morphological changes of apoptotic cells were observed with fluorescent and electronic microscope;terminal deoxynucleotidyl transferase dUTP nick end labeling(TUNEL)assay,flow cytometry,and Western blot were employed to assess the inhibition and apoptosis of MCF-7 cells.Results The growth of MCF-7 cells was inhibited by β-ionone with the inhibitive rates of 6.57%,34.58%,65.22%,and 81.87%at the doses of 25,50,100,and 200 μmol/L,respectively,after 7 days' treatment.The morphological changes of apoptotic MCF-7 cells treated with different concentrations of β-ionone were observed.The frequency of apoptosis ascertained by TUNEL assay and flow cytometry showed an increasing trend with the increment of β-ionone concentration.The aoptosis index(AI)was 20.74%(24 hours after the treatment)and 33.15%(48 hours after the treatment)with TUNEL assay,and 27.96%(24 hours after the treatment)and 38.59%(48 hours after the treatment)with flow cytometry.The expressions of proliferating cell nuclear antigen(PCNA)and bcl-2 protein were inhibited in a dose-dependent manner.Conclusion β-ionone could inhibit the cell proliferation and induce apoptosis in MCF-7 cells and its exact mechanism needs to be studied further.