This study aimed to investigate the diagnostic predictive value of R wave peak time (RWPT) in patients admitted to the emergency department with a preliminary diagnosis of acute pulmonary embolism (APE). Computerized tomographic pulmonary angiography (CTPA) was performed in 74 consecutive patients with suspected APE, and of these 66 patients with appropriate electrocardiogram (ECG) and CTPA images composed the study population.By using CTPA, APE was confirmed in 27 patients. While the atrial arrhythmia, right axis deviation, complete or incomplete right bundle branch block, prominent S wave in the lead DI, S1Q3T3 pattern, and RWPT in the lead DIII (40±11 vs. 31±13 ms) were statistically different in patients with APE compared to those without APE (p<0.05, for all), the other ECG findings were similar. Multivariate analysis revealed that RWPT in the lead DIII (odds ratio: 14.959, 95% confidence interval: 1.811-123.582, p=0.012) was found to be an independent predictor of APE. A receiver operating characteristic analysis was drawn to show the best cutoff value of the RWPT in the lead DIII to predict APE was ≥40 ms with 48.1% sensitivity and 87.2 % specificity (area under curve (AUC): 0.718; 95% CI: 0.593-0.843; p=0.003).The present study demonstrated that the RWPT in the lead DIII may have diagnostic predictive value for APE. In addition, it may be useful in electrocardiographic signs for the diagnosis of APE.