Abstract: Objective To summarize the clinical characteristics and diagnosis of rectosigmoid endometriosis and improve clinical practice. Methods Imaging and clinical data about 13 patients with suspected colorectal endometriosis who were confirmed as rectosigmoid endometriosis by postoperative pathology in the department of ultrasound of Chinese PLA General Hospital from January 2010 to December 2017 were retrospectively analyzed. Results Of the 13 patients with average age of (38±7) years old(ranging from 26 to 47 years), the muscular layer was involved in 11 cases, rectal serosa layer in 1 case, and mucosal layer in 1 case; 3 cases received partial resection of the rectal wall lesions, 9 cases underwent resectorial anterior resection of the lesion, while 1 patient had no intraoperative treatment. The intestinal wall of all patients were stiffness by rectal examination, and one patient with mucosal layer involvement demonstrated firmness on mucosal surface. Eleven cases were diagnosed by ultrasound, 2 cases were missed diagnosis; 5 cases were examed with MRI, and 4 cases were diagnosed, 1 case was missed diagnosis. The typical sonographic features were thickened rectosigmoid wall, lesions manifested as hypoechogenic nodules with obtuse margins that were attached to the intestinal wall, C-shaped segment of the colon and extrinsic compression of the bowel. In the axial plane, rectal lesions showed a typical pyramidal shape, with the base adhering to the anterior rectal wall and the apex oriented toward the retrocervical space.Color Doppler ultrasound showed that blood flow signals were hardly to be detected in the lesions. Conclusion Rectosigmoid endometriosis has typical sonographic feature, mainly characterized by irregular thickening of the rectal wall. When the patient has periodic irritability or rectal pain, it needs to be alert to the presence of rectosigmoid endometriosis.