A 32-year-old woman with chronic schizophrenia who took 8-10 liters of water for three years due to thirsty, admitted to our hospital because of convulsion and muscle weakness. Neurological finding on admission showed a mild disturbance of consciousness, moderate proximal muscle weakness, and muscle pain. Laboratory examination revealed marked serum hyponatremia(102 mEq/l) and high value of creatin kinase (1,259 IU/l). The level of creatin kinase reached a peak(39,700 IU/l) at the 5th hospital day. An analysis of the muscle biopsy specimen showed necrotic muscle fibers and opaque fibers, that was compatible with rhabdomyolysis. T 2 weighted magnetic resonance imaging of the brain showed a transient high signals in bilateral putamen but not in pons. She was diagnosed to have rhabdomyolysis due to water intoxication. The present case is the first rhabdomyolysis in Japan that was confirmed by muscle biopsy at an acute stage of water intoxication related with schizophrenia.