Cancer growth follows fine balance disturbance between cell proliferation, differentiation and death. It has been shown that mutation of 4 to 5 genes controlling cellular proliferation events may be contributive to carcinogenesis. Estrogens play a central role in reproductive physiology. They are also a causative factors in the pathogenesis of neoplastic and non-neoplastic diseases, including breast cancer. The estrogen dependency of human breast cancer has been successfully exploited in the treatment of early and advanced diseases and provides a unique opportunity for chemoprevention of this common malignancy. The aim of present study was to examine the effects of tamoxifen and raloxifen on the induction of apoptosis and proliferative activity of human breast adenocarcinoma MCF-7 cells. It has been found that both tamoxifen and raloxifen decreased the speed of cell cycle in MCF-7 cells and acts as proapoptotic factors. It reduces viability of cancer cells and probability of neoplastic clone multiplification. This effect conducts to limitation of cancer expansion.