Objectives: Our aim was to compare the cytotoxic effects of tamoxifen and docetaxel, currently used in breast cancer treatment, and ukrain, which demonstrates antiproliferative properties on breast cancer cells. Methods: MCF-7 and MDA MB-231 cells were treated with various doses of docetaxel, tamoxifen, and ukrain. The cytotoxic effects of all drugs were determined with the cell empedance technique. Cell blocks were prepared from cultured and drug-exposed cells for histopathological and immunohistochemical determinations of Ki-67, Bcl-2, Bax, and Cyclin-D1 expressions. Results: According to comparisons of proapoptotic and antiapoptotic protein expression indices, no statistically significant difference was found between the effects of ukrain and docetaxel in both cell lines. Although tamoxifen was more effective than ukrain in MCF-7 cells, ukrain was also more effective than tamoxifen in MDA MB-231 cells for inducing apoptosis. Conclusions: Although ukrain presented antiproliferative and apoptotic effects on both cell lines, MDA MB-231 cells were more vulnerable to the effects of ukrain. The findings suggest that ukrain might be a useful therapeutic agent, especially for treating receptor-negative breast cancer cells.