A 34-year-old man presented with paroxysmal hypogastralgia during defecation for 2 weeks. Physical and laboratory examination findings were unremarkable, other than a depression located 1 cm above the dentate line, accompanied by mild tenderness and a clubbed induration extending to the rectum. Colonoscopy showed a 2.0×0.8 cm longitudinal, protruding mass in the posterior wall of the lower rectum. Endosonography revealed a mixed echogenic mass originating from the rectal submucosa, with no sign of muscular wall disruption. There was no evidence of Crohn's or other diseases. Following anorectal consultation, we suspected a submucosal or internal blind fistula since the patient was symptomatic with a superficial mass which communicated to the rectum. The location and depth of the mass indicated that endoscopic resection might allow for removal of the lesion without impairment of the anorectal anatomy and function. After obtaining the patient's consent, endoscopic submucosal dissection (ESD) was performed. En bloc resection was achieved using a disposable, high-frequency knife (Micro-Tech, China). No adverse events occurred. Histopathological examination revealed a benign fistula composed of local submucous granulomatous tissue proliferation and a focal mucous epithelial defect. The patient's symptoms were relieved postoperatively, and no recurrence was evident after 6 months.