PURPOSE: Ulcerative colitis (UC) is a chronic, nonspecific inflammatory bowel disease primarily affecting the colorectal mucosa. The disease is characterized by a relapsing-remitting course and is currently incurable. Its pathogenesis is multifactorial, involving genetic predisposition, environmental triggers, immune dysregulation, and alterations in gut microbiota. The appendix plays a role in modulating intestinal immunity and maintaining microbial homeostasis. Left-sided colitis with appendiceal orifice inflammation (AOI) or periappendiceal erythematous patch (PARP) is a common endoscopic finding in UC. However, whether AOI in UC patients requires intervention remains debated. METHODS: Here, we report a rare case of a UC with AOI. RESULTS: By means of cholangioscope-assisted endoscopic retrograde appendicitis therapy (ERAT), copious purulent secretions were discovered and flushed out of the appendiceal cavity, resulting in clinical remission and endoscopic mucosal healing of UC. CONCLUSION: Our case indicates that there may be some correlation between the appendix and the pathogenesis of ulcerative colitis. For refractory left-sided UC patients with AOI, ERAT-based management of appendiceal lumen inflammation may benefit patients.