We report a case of Wernicke's encephalopathy after sleeve gastrectomy, which had been complicated by stomach wall edema and aggravated by dietary non-compliance. Despite intense parenteral nutrition, thiamine deficiency became clinically evident. It suggests that nutritional preparations used were unable to cover the increased thiamine requirement. After intense thiamine supplementation, gradual improvement occurred during the 6 months after the diagnosis, without permanent cognitive impairment. Clinicians involved in postoperative management of bariatric surgery patients must consider Wernicke's syndrome in hyper-emetic patients, who show unclear neurological deterioration. Early diagnosis and treatment can instantly improve the patient's condition without permanent sequelae.