Abstract： Objective To evaluate the association of expressions of leptin and leptin receptor in breast cancer with tumorigenesis and development and clinicopathologic factors.Methods The expression of leptin and leptin receptor was performed in 132 cases of breast cancer,66 cases of benign breast lesions,and 30 cases of corresponding normal breast tissue by using immunohistochemical methods. Results The expressions of leptin and leptin receptor were 76.5 ％ (101/132) and 70.5 ％ (92/132).It was significantly higher than that in benign breast lesions 56.1％ (37/66) and 56.1％ (37/66),and corresponding normal breast tissues 46.7 ％ (14/30) and 43.3 ％ (13/30) (x2 =8.72,P =0.003,x2 =4.04,P =0.044,x2 =10.57,P =0.001and x2 =7.94, P =0.005).The level of leptin expression showed a significant correlation with the level of leptin receptor (r =0.307,P ＜ 0.05).The expression of leptin and leptin receptor in breast cancer tissue were not significantly related to ages,menopause,tumor size,classification,pathological type,distant metastasis,ER and PR expression (P ＞ 0.05).The positive rate of leptin in patients with lymph node metastasis was 91.7 ％,which was significantly higher than that in patients without lymph node metastasis (67.9 ％,x2 =10.65,P =0.002).Conclusions The expressions of leptin and leptin receptor have a significant correlation with breast cancer and may have the promoting effect on the carcinogenesis and development of breast cancer.