Objective:To identify the expression of leptin receptor in breast cancer cell line MCF-7, and to explore the effects and mechanisms of leptin on the anti-proliferative effect of tamoxifen on MCF-7. Methods:The expression of leptin receptor was detected by immunofluorescence and Western blot. After treated with 100 ng/ml of leptin and 1 000 nmol/L of tamoxifen(TAM), cell proliferation and the levels of estrogen receptor α(ERα) in MCF-7 were examined. Plasmid pERE-LUC which containing estrogen response element(ERE) and reporter gene luciferase was constructed and transfected into MCF-7 cells, the expression of luciferase was detected to reflect the effects of leptin on the transcription of ERα. Results:Leptin receptor was positively expressed in MCF-7 cells. Leptin weaken the inhibition of TAM on MCF-7 proliferation by upreglulating the transcription of ERα. Conclusion:Leptin could interfere with the inhibition of TAM on breast cancer cells, it may contribute to the efficacy of tamoxifen treatment for breast cancer patients.