We present a female patient with sigmoid colon endometriosis who was diagnosed correctly preoperatively and underwent minimally invasive surgery. She was admitted to our hospital with rectal bleeding and constipation. We performed several workups. Colonoscopy and endoscopic ultrasonography showed sigmoid colon stenosis caused by submucosal tumor, and magnetic resonance imaging revealed a sigmoid colon tumor displaying signal hypointensity on both T1- and T2-weighted imaging. However, colonoscopic ultrasonography-assisted needle aspiration biopsy could not specify tumor characteristics. From these examinations, the lesion was diagnosed as sigmoid colon endometriosis and laparoscopy-assisted sigmoidectomy was performed. Pathological diagnosis from the resected specimen was identical to preoperative diagnosis, i.e., colonic endometriosis. Since differential diagnosis of intestinal endometriosis seems difficult, a cautious preoperative diagnosis is required to select treatments including minimally invasive surgery.