Carbamazepine is a commonly used anticonvulsant and is generally considered to be a safe drug. However, it may sometimes be responsible for some serious toxic effects and even deaths. A 14 month-old girl patient was hospitalized because of convulsion. General condition of this patient without a history of trauma was moderate and her consciousness was lethargic. The patient without other risk factors and a history suggestive of intoxication was admitted to hospital for observation of the clauses of seizure. The patient's mother was epileptic and had a history of using carbamazepine. Carbamazepine can seriously induce hyponatremia. At children's cases with evidence of poisoning but not be shown, drugs used by parents should be investigated.