Hydrogen peroxide is a compound consisting of oxygen and hydrogen.Esophageal fistula is known to be a late complication of corrosive ingestion, but no case was reported. Thus we are reporting a case of a delayed esophageal fistula that is treated with surgery, which occurred after ingestion of hydrogen peroxide while conservative treatment. 40-year-old male patient was found to have fallen with decreasing mentality and admitted to the emergency room. he was drowsy mental state, and perioral redness with ulcer and brownish vomitus were observed. According to the witness, the patient swallowed 200cc of undiluted hydrogen peroxide (35%) accidentally and vomited. At time of admission the status was BP 140 / 86mmHg, PR 140 beats/min, RR 84 beats/min, temperature 36 degrees, and saturation 92%, respectively. Although physical examination did not show wheezing, intubation was done due to substantial airway secretions.arterial gas examination resulted in pH7.33, pCO2 25mmHg, pO2 76mmHg, HCO3- 13.2mmol/L, oxygen saturation 94%, indication metabolic acidosis and hypoxia. Nasogastric tube was inserted to decompress GI tract, and brown gastric juice was drained. Thoracic and abdominal CT was normal finding. Patient was admitted to ICU for conservative treatment. At 14th day empirical antibiotics were given to treat uncontrolled fever and increased sputum, but since the symptoms are not alleviated, thoracic CT was taken in order to evaluate pneumonia. As the result a new trachea-esophageal fistula was found at lower trachea and around the left main bronchus. he was transferred to emergency thoracic surgery and was discharged after 52 days of admission. Ingesting corrosives could result in delayed trachea-esophageal fistula, and misdiagnosing it for aspiration pneumonia or neglecting it could lead to fatal consequences. Thus for fever and inflammation unresponsive for antibiotics, an active examination through thoracic CT is recommended.