The authors described a case of male schizophrenia who developed myoclonic jerk repeatedly and one episode of convulsive seizure during the treatment of clozapine. According to literatures and reported cases, myoclonic jerks induced in a small amount of clozapine may precede and predict the development of a convulsive seizure. Therefore clinicians have to pay attention to the development of a myoclonic jerk during the administration of clozapine. They may decrease the dosage of clozapine step by step at first in the convulsive state, and observe EEG changes of patients frequently.