Objective: To investigate the cause of misdiagnosis of mucinous tumor of appendix by ultrasonography.Methods:The ultrasonographic findings of 13 patients with mucinous tumor of the appendix who were treated in our hospital from April 2014 to April 2018 were retrospectively analyzed.Results:Among the 13 patients, the characteristics of two-dimensional ultrasonography were as follows: 4 patients, the characteristics of two-dimensional ultrasonography were as follows: 4patient presented with massive hypoechoic mass in peritoneal cavity with abdominal effusion. 1 case showed no echo in the right accessory area and poor tension. 5 cases showed mixed echo dominated by cystic in the right accessory area. 3 case presented as a typical case of right lower quadrant appendiceal enlargement with a blind hypoechoic tubular structure with a few anechoic areas around. The ultrasonographic diagnosis was as follows: 9 patients were diagnosed as malignant tumors of ovarian origin; 1 patient was diagnosed as a cystic mass of oviduct origin. 3 patient was diagnosed with acute appendicitis and had peripheral exudation.Conclusions: Appendiceal mucinous tumor is a rare disease. Ultrasonic sonogram is not typical. When the lesion size is large, ultrasound is difficult to accurately locate, and it is extremely difficult to differentiate from tumors of the right ovary and oviduct origin. For patients with relatively small size of lesions, although ultrasound can relatively accurately locate the source of lesions, it is easy to be misdiagnosed as appendicitis due to the overlapping of ultrasonography and inflammatory changes in the appendix. Therefore, other imaging diagnosis can be used as a supplement for the patients whose ultrasound cannot accurately locate and suspected appendicitis