Abstract: To investigate the antiproliferative effect of betulin and betulinic acid on 3 kinds of human cancer cells and the mechanism of betul inic acid induced cytotoxicity in MCF7 cell line, crystal violet dyeing was used to screen the cytotoxicity effect of betulin and betulinic acid in the cancer cells. RTPCR was operated to determine the expression of p21 mRNA, p53 mRNA, Bcl2 mRNA and Bax mRNA. This study shows that the growth of tumor cells is significantly inhibited by betulin and betulinic acid in dosedependence. The study alsoindicates that betulinic acid induces the apoptosis of MCF7 cells. So a s to make the expression of p21 mRNA and p53 mRNA increased but make the express ion of Bcl2 mRNA and Bax mRNA unchanged.

Key words: betulin, betulinic acid, cell cycle, apoptosis