Abstract: Objective To determine the value of precordial leads for differentiating the origins of outflow tract idiopathic premature ventricular contractions arrhythmias. Methods The features of electrocardiogram in 112 patients with ventricular premature beat originated from ventricular outflow tract (RVOT, n=82; LVOT, n=30) who had undergone successful catheter ablation from September 2013 to September 2016 in our hospital were analyzed. The R-wave transition in precordial leads and V₂S/V₃R index were recorded and their diagnostic accuracies for the origins were calculated. Results Of the 112 patients, 40 cases had the R/S transition after leads V₄ (including V₄), and the specificity of the R/S transition after lead V₃ for predicting the origin from LVOT was 48.8%, while the sensitivity was 100%. The other 72 patients were further studied by V₂S/V₃R index. When the V₂S/V₃R index was under 1.5, it predicted LVOT origin with sensitivity of 92.9% and specificity of 93.2%. Conclusion The R-wave transition in precordial leads and V₂S/V₃R index can differentiate the origins of outflow tract ventricular arrhythmias, which has a great value for guiding catheter ablation.