Calcium oxide is commonly used as a desiccant for food in Japan. Calcium oxide, reacting with water, changes into calcium hydroxide and releases heat. Calcium hydroxide is a strong alkaline and seriously damages mucosa and skin together with heat. We report a rare case of a corrosive injury of the esophagus and larynx caused by calcium oxide. A 67-year-old male accidentally swallowed calcium oxide, mistaking it for a cookie. After 6 hours, he complained of dyspnea and dysphagia. An upper gastrointestinal endoscopic examination revealed an ulcer of the upper esophagus and edema of the pharynx and larynx. He underwent a tracheostomy and was treated with prednisolon, aluminum hydroxide and magnesium hydroxide and recovered with no complications.