Objective To investigate risk factors of corrected QT (QTc) interval prolongation in schizophrenia pa-tients treated with clozapine. Methods Two hundred and ten schizophrenia patients treated with clozapine were included in the study. Measurement of myocardial enzymes and electrocardiography were performed to determine QTc interval. QTc interval was calculated according to Bazett’s formula. Results QTc prolongation prevalence rate was 15.24%, The QTc prolongation prevalence rate was higher in female than in male (29.23%vs. 8.98%, P<0.001). The mean QTc inter-val was longer in female than in male [(427.30 ± 24.33)ms vs. (410.39 ± 25.80)ms, P<0.001]. The QTc interval showed weak positive correlation with age (r=0.203, P=0.003) and heart rate (r=0.326, P<0.001). There was no correlation be-tween QTc interval and clozapine dosage or therapy course (P>0.05). Multi-factors linear regression analysis showed that heart rate was related with QTc interval (β=0.719, standardizedβ=0.691, P=0.027). Conclusions QTc interval prolonga-tion prevalence rate is high in patients treated with clozapine. And increased heart rate might be risk factor of QTc inter-val prolongation.