Background It is essential to clarify the interactions of hormones during the progression of human breast cancer. This study examined the effects of exogenous human leptin on estrogen receptor (ER) α and β in human breast tumor tissue in a nude mouse xenograft model.Methods We created nude mice xenografts of MCF-7 human breast cancer cells, and randomly divided them into an experimental group and a control group. The mice in experimental group were injected subcutaneously around tumors with human leptin, while the control group were injected with the same dose of normal saline. A real-time RT-PCR assay was developed to quantify the mRNA of Erα,β in the tumor tissues. Western blotting analyses were used to assess the relative quantities of the Erα,β proteins.Results Leptin-treated xenografted nude mice were successfully established. The amount of Era mRNA was significantly higher in the leptin group than in the control group (P<0.01), while the amount of Erβ mRNA was significantly lower in the leptin group than in the control group (P<0.01). Western blotting analyses revealed that the Erα protein level was significantly higher in the leptin group than in the control group (P<0.01), while the Erβ protein level was significantly lower in the leptin group than in the control group (P <0.01).Conclusions Nude mouse xenograft model can be safely and serviceably treated with human leptin by subcutaneous injections around tumor. Erα,β were both targets of leptin in breast cancer. Leptin can up-regulate the expression of Erα and down-regulate the expression of the Erβ in human breast tumor.