Although thermal esophageal injuries caused by hot food or tea have been reported, thermal esophageal injury due to sodium picosulfate with magnesium citrate (PSMC) used for bowel preparation is rarely reported. We report the case of a 56-year-old man who presented with esophageal injury after ingestion of PSMC. Instead of dissolving the PSMC in water before ingestion, he drank water immediately after swallowing PSMC powder. As soon as he drank water, he developed severe chest pain and hematemesis. Upper endoscopy revealed severe hemorrhagic, ulcerative mucosal change from upper to mid-esophagus. He was hospitalized for nine days, received conservative treatment (fasting and parenteral nutrition), and recovered without complications. When PSMC is used as a colonic cleansing agent, patients should be educated to take it after dissolving it sufficiently in 150 mL of water to avoid esophageal thermal injury.