Dehumidifying agents are commonly used to remove moisture and odors and are not meant for oral ingestion. The hazards of accidental oral ingestion of dehumidifying agents are not well known. A 31-year-old man with autism drank the liquid desiccant contained in the barrel of a dehumidifier while sleepwalking. The desiccant mainly consisted of calcium chloride. He was taken to the emergency center with persistent vomiting and underwent gastric lavage. The patient was treated for hypercalcemia due to calcium chloride poisoning. He eventually died of multiple organ failure. Autopsy findings were as follows: acute suppurative pneumonia, intra-abdominal inflammation, liver necrosis, acute pancreatitis, and gastrointestinal hemorrhage. Calcium chloride has relatively low toxicity; however, when ingested orally, it can cause severe internal damage, and even death. We suggest active preventive measures to ensure the safe use of dehumidifying agents.