Objective To explore the relationship between diagnostic accuracy of mammography, ultrasound and female body mass index (BMI), breast volume, breast density in breast cancer. Methods We retrospectively analyzed 1101 cases of female patients who were confirmed by operation and pathology. All patients underwent mammography and ultrasonography before operation.BMI were ranged from 16.23 to 40.01 kg/m2, with an average of (24.42 ± 3.45) kg/m2. Diagnosis was based on mammography and ultrasonography imaging, and the pathologic diagnosis was as gold standard. The diagnostic efficacy of different imaging methods was analyzed. The patients were divided into diagnostic accuracy group, false negative group and false positive group according to the imaging results. The differences of BMI, breast volume and breast density between 3 groups were compared by t test. Pearson method was used to evaluate the the correlation between BMI, breast volume and mammary gland density measured by mammography. Results The mammography diagnosis of accuracy group, false negative group and false positive group were 1 011, 40 and 50 cases respectively. The diagnostic sensitivity, specificity and accuracy were 94.2%(655/695), 87.7% (356/406) and 91.8% (1 011/1 101) respectively. The ultrasound diagnosis of accuracy group, false negative group and false positive group were 1 006, 34 and 61 cases respectively. The diagnostic sensitivity, specificity and accuracy were 95.1% (661/695), 85.0% (345/406) and 91.4% (1 006/1 101) respectively. The results of Pearson correlation analysis showed that BMI was positively correlated with breast volume (r=0.562, P 0.05). There were no significant differences in breast density, breast volume and BMI between false negative group and the false positive group of ultrasonography (P>0.05). Conclusions Lower BMI, higher breast density and smaller breast volume may lead to false-negative results. There was a correlation between BMI and breast volume, suggesting that BMI had a potential to indirectly reflect breast volume. Key words: Mammography; Ultrasonography; Body weight; Breast density; Breast volume