Purpose: To study the influence of estrogen on the proliferation of human carcinoma cells. Methods: Treated with different concentrations of estrogen, the influence of estrogen on MCF7 was detected by MTT test. Several proteins related with cell cycle, tumor suppressor, proliferation and apoptosis were detected by the method of Western blot. Results: MTT test showed that estrogen could promote the proliferation of MCF7. Cyclin Dl was increased at the same time. But the protein level of PTEN, a tumor suppressor gene, was not changed by estrogen. Furthermore, as an anti -apoptotic protein, PKB protein level was also unchanged. Conclusions: Estrogen can promote the proliferation of human carcinoma cells by certain pathways including cyclin Dl, but not including PKB.