Objective To investigate the prolongation and related factors of antipsychotic drugs on QTc interval in first-episode mental disorders. Methods A retrospective study of 309 first-episode patients with mental disorders treated with one month stable dosage of antipsychotics was conducted. The demographic data， the electrocardiograms（ECG） data， fasting blood glucose， blood pressure， blood lipids and other biochemical indicators were collected， and the prolonged QTc interval and its related factors were analyzed with QTc ≥440 ms as the standard of QTc prolongation. Results The incidence of QTc interval prolongation was 10.6%. The mean value of QTc interval in the drug treatment group was higher than the baseline period， with statistical difference （P＜0.05）. There was no significant difference in QTc interval either in the drug combined electroconvulsive therapy group or drug combined electroencephalography treatment group compared with the baseline period（ P＞0.05）. Also there was no significant difference in QTc interval between the single antipsychotic group and the baseline （P＞0.05）. The mean value of QTc interval either in the combination of antipsychotics or antipsychotics combined with antidepressants/mood stabilizers was higher than baseline， and the difference was statistically significant （P＜0.05）. There was significant difference in the QTc interval between the antipsychotic equivalent chlorpromazine dose（ ＜1 000 mg/d） group and the baseline period（ P＜0.05）. There was no correlation between antipsychotic dosage and QTc interval. The gender of female were a risk factor of QTc prolongation（ OR=3.26，95%CI=1.050-10.094）， and other factors were not included in the regression equation. Conclusions There is a gender difference in the QTc interval prolongation during antipsychotic treatment for first-episode mental disorders， and the risk of QTc prolongation in female is 3.26 times greater than male that in. The prolongation of the QTc interval of drug combination does not reach the abnormal value. There is no correlation between antipsychotic dosage and QTc interval. In addition to gender factors， other parameters are not the risk factors of QTc prolongation.