A 30-year-old man was admitted due to decreased mentality. He was diagnosed as a diabetic ketoacidosis by hyperglycemia, metabolic acidosis, and positive urinary ketone bodies. Two weeks later, despite the improved state of ketoacidosis, he complained of dysphagia, quadriparesis, and respiratory difficulty. Cerebrospinal fluid analysis showed albumino-cytologic dissociation. Nerve conduction study revealed axonal motor neuropathy. His neurological deficit was rapidly improved by intravenous immunoglobulin. We report a case of Guillain-Barre syndrome just after a ketoacidosis.