Solitary rectal ulcer syndrome (SRUS) is a rare disorder characterized by rectal ulceration associated with typical histological features and disturbed defecatory behaviour from the passage of blood and mucus. While the cause of SRUS is yet unknown, the rectal prolapse and the paradoxical contraction of pelvic floor muscles have been considered the most important factors. The diagnosis is made usually on the basis of clinical symptoms, endoscopic appearance, and histology. Despite the terminology of SRUS, patients often show multiple lesions instead of just a single lesion or polypoid lesions instead of ulcerative lesions. Polypoid lesions, especially when combined with histologic findings of colitis cystica profunda, may sometimes be mis-interpreted as cancer. We report the case of one female patient with SRUS with out-growing polypoid lesion, which was misdiagnosed as invasive cancer on endoscopic biopsy.