A 43-year-old man was admitted with end-stage renal disease caused by IgA nephropathy, and was treated with maintenance peritoneal dialysis. The patient developed general fatigue and appetite loss, and his symptoms were gradually aggravated by depression. After approximately 2 months on dialysis, the patient presented with altered consciousness and ophthalmoplegia. Wernicke's encephalopathy was diagnosed based on the presence of classic symptoms and the findings on magnetic resonance imaging. Thiamine replacement therapy was immediately initiated. The patient recovered from most of his neurological symptoms; however, the sequela of Korsakoff syndrome remained. A marginal thiamine deficiency in combination with predisposing factors must be considered when treating dialysis patients.