A Japanese woman in her 40s came to our emergency room with vomiting and upper abdominal pain after drinking a bottle of milk tea at home. She had a history of bipolar disorder. Blood tests revealed hypercalcemia (calcium level of 18.6mg/dl). Abdominal computed tomography depicted thickening of the gastric wall and hyperabsorbed material in the stomach. Upper gastroduodenal endoscopy showed extreme mucosal redness from the gastric body to the pylorus. The hypercalcemia improved with intravenous infusion of zoledronic acid. The patient had not been taking any medication that could have caused hypercalcemia. Later, her father drank the same bottle of milk tea at home and developed upper abdominal pain. He was admitted to the hospital because of vomiting, and computed tomography showed hyperabsorbed material in the stomach, as in his daughter's case. Computed tomography of the bottle of milk tea revealed a highly absorbent substance. The bottle was sent to the forensics laboratory for testing, and it was found to contain calcium chloride. Thus both patients had consumed a beverage containing calcium chloride, and corrosive gastritis was diagnosed. Despite fasting and intravenous drip therapy, the first patient underwent a total gastrectomy because of severe stenosis and perforation of the gastric lumen.