Objective:To determine the ultrasound imaging features of mammary ductal ectasia(MDE). Methods:The sonographies and clinical characteristics of 52 patients with MDE confirmed by pathology were studied retrospectively. Result:① According to the ultrasound imagines of 52 cases,MDE could be classified into four types: type Ⅰ,duct dilatation(2%); type Ⅱ,cystosolid mass within or around the duct (53.8%);type Ⅲ,hyperechoic or heterogeneous-echoic mass with a hypoechoic rim(19.2%);and type Ⅳ,partly or fully fludified abcess(26.9%). ② The two peaks of incidence were at 30~40 or 50~60 years. Most of the lesions(84.6%) were around the areola(44/52),34.6% of patients with inverted nipple(18/52),and 53.8% with duct dilatation (28/52). ③ The rate of preoperative diagnosis of inflammatory masses was 88.5%(46/52). The diagnostic accordance rate of acute and subacute inflammation was 95%. Conclusion:The appearances of MDE are complicated. It would be misdiagnosed if judged only by sonographic features. Combination with clinical characteristics could improve the accuracy rate of diagnosis. Acute and subacute cases could be diagnosed easily,while chronic cases were harder to be diagnosed.