Objective To investigate ultrasonographic (US) features of mucinous breast carcinoma with pathological correlation and to improve the early diagnosis for the mucinous breast carcinoma.Methods Twenty-two patients with 23 focuses mucinous carcinoma of the breast confirmed by pathology were included in this study,retrospectively evaluate sonographic features according to the American College of Radiology(ACR) Breast Imaging Reporting and Data System(BI-RADS) Lexicon,all cases were classified by BI-RADS before operation.Histological type of mucinous breast carcinoma included mixed and pure two forms,the latter was classified into cellular variants and hypocellular variants.The correlation between the ultrasonographic findings of mucinous carcinoma and histologic features in different types were analysed.Results On US examination,all 22 cases presented as solid mass.In pure form,they showed well-defined margins with no pseudocapsule and isoechogenic or hypoechoic internal echo pattern relative to that of subcutaneous fat in 86.7％ (13/15) focuses which histological type were pure type.93.3％ (14/15) of pure type focuses had posterior enhancement.All pure type focuses demonstrated that the orientation of the mass is parallel to the skin line.75.0％ (6/8) of mixed type focuses and 13.3％ (2/15) of pure type focuses,however,demonstrated ill-defined and or spiculated margins with more hypoechogenic structure (P ＜0.01).Mixed type focuses have more aggressive malignant features.65.2％ (15/23) of cases being classified as BI-RADS 4 or 5 were suspected as malignancy,which included 6 mixed type focuses and 9 pure type respectively accounting for 75.0％ (6/8) and 60.0％ (6/15) of each type focuses.Conclusions Mucinous breast carcinoma especial pure type did not have the typical malignant breast masses sonographic features,which showed some benign masses sonographic features except no pseudocapsule benign feature.Mixed type mucinous carcinomas tumors have more aggressive margin imaging characteristics.It is suggested that mucinous breast carcinoma should be classified category 4 by BI-RADS to avoid diagnosis delay.