Objective To study the mechanism of chemopreventive effect of ursodeoxycholic acid(UDCA)on human colon adenocarcinoma cell line Caco-2 in vivo.Methods UDCA preparations of different concentration were used in culture of human colonic adenocarcinoma cell line Caco-2,and their effects on cellular proliferation and apoptosis were observed.Results Cell proliferation and apoptosis were blocked by UDCA,which showed a significant positive association with the concentration and the duration of UDCA treatment.Conclusion UDCA produces a restrictive effect on cancer cell proliferation and enhances apoptosis in vivo.