Hydrogen peroxide is commonly used as a disinfectant that has been reported to cause chemical colitis. We report a case of 49 year-old man who presented with chemical colitis caused by self-inflicted hydrogen peroxide enema. In the sigmoidoscopic examination, diffuse erythematous and edematous mucosal change with multiple ulcerations and easy touch bleeding was noted from the rectum to the proximal sigmoid colon. Abdominal computed tomography showed diffuse wall thickening of the rectum and the sigmoid colon with inflammatory and reactive change at surrounding. The patient was treated with NPO, intravenous fluid, and antibiotic therapy. On 5th hospital day, abdominal pain and bloody stool disappeared, and the patient started oral feeding. He discharged on 6th hospital day with fully recovered state. (Korean J Gastroenterol 2011;58:100-102)