Objective To determine whether arsenic has estrogen-like effects,the cell proliferation was measured iil human eervical cancer line(HeLa)in vitro.Methods The HeLa cells were grown in improved RPMI 1640 supplemented respectively with β-estradiol(E2,1 nmol/L),Arsenic trioxide(As2O3,0.5,1.0,5.0 μmol/L),ICI (500 nmol/L),E2(1 nmol/L)+ICI(500 nmol/L),As2O3(1.0 μmol/L)+ICI(500 nmol/L)and control.The growth morphology of HeLa cell was observed under microscope after 72 h.The method of M1Tr was used to study the cell proliferation after 24.48 and 72 h.The technique of flow eytometry was used to measure cell cycle after 48 h. Results HeLa cells in E2 and 0.5 μmoL/L As2O3 treatment were more better growth in morphology than control group.Percentage of HeLa cells proliferation at 24,48,72 h in E2 and 0.5 μmol/L As2O3 treatment were 6.35%, 11.56%,38.33%and 6.35%,8.50%,20.26%respectively.The proliferation effect of HeLa cells was similar in two treatments.The proliferation of HeLa cells were inhibited in other treatments.Compared with control[(41.68± 1.05)%],HeLa cells were promoted go to S phases in E2[(55.72±2.31)%]and 0.5 μmol/L As2O3[(47.82± 1.41)%]treatment.But in other treatments HeLa cells were hold back to S phases.Compared with control,there was a significant differenee(P＜0.05)of cell percentage in S phases in 5.0 μmol/L As2O3[(21.11±4.99)%]and ICI[(20.16±4.76)%]treatments.Conclusion Small amounts of As2O3 impose estrogen.1ike effects and stimulate the proliferation of HeLa cells.