Objective: To investigate the relations of body mass index (BMI) with the prevalence and the clinicopathologic features of breast cancer. Methods: The BMI values of 413 female patients (breast cancer group) with breast cancer and 425 healthy women (control group) undergoing routine screening during the same period were compared without and with stratification by age (<60 vs. ≥60), and the relation of age and BMI value with the prevalence was analyzed by logistic regression. In addition, the relations of BMI with the clinicopathologic factors of breast cancer patients were analyzed. Results: The BMI value of breast cancer group was significantly higher than that of control group [(25.80±3.57) kg/m2 vs. (25.28±3.19) kg/m2, P=0.029] in general however, the BMI difference was only found lying in the population aged over 60 years old after age stratification (Z=–3.408, P =0.001). Logistic regression analysis demonstrated that the risk of breast cancer was significantly increased as the BMI value exceeded 30 kg/m2 (OR=1.892, 95%CI=1.125–3.181, P=0.016), while age yielded no obvious influence on the risk of breast cancer (P>0.05). BMI was related to the axillary lymph node metastasis and expression status of Her-2/neu (both P<0.05), but unrelated to the tumor size, histological grade or ER and PR status of the breast cancer patients (all P>0.05). Conclusion: BMI is associated with the prevalence of breast cancer in our country. Determination of BMI is helpful for screening a population at high risk of breast cancer, so as to provide useful information for aggressive prevention, estimation of prognosis and administering of a suitable treatment plan.