Introduction: Long procedure time is always major concern of using Carto-Merge (CM) mapping system for ablation of atrial fibrillation (AF). So we pursued easy and time-saving left atrium (LA) electroanatomic mapping (EAM) method and assessed accuracy of simplified method of CM. Methods: Forty patients undergoing AF ablation using CM mapping system were enrolled in the study. Only pulmonary veins (PVs), posterior LA wall and roof mapping was performed in 20 patients (group I), and whole LA mapping was performed in the other 20 patients (group II) for merge. For both the groups, we compared total mapping time and number of mapping points, surface-to-point distance for mapping points (mean distance between the 3D CT surface and all EAM points at pre-ablation), and ablation surface-to-point distance for circumferential PV ablation points. Results: Baseline characteristics of age, sex, past history, and echocardiographic parameters including left ventricular ejection fraction and LA diameter were not different between the two groups. Paroxysmal AF was 16 (80%) patients in group I and 20 (100%) patients in group II. Group I showed significantly shorter total mapping time (29짹9 vs. 56짹11 minutes) and less total mapping points (159짹46 vs. 340짹52 points) than group II (p <0.01). Furthermore, for surface-to-point distance of mapping points and ablation surface-to-point distance, group I showed more efficient merge than group II (1.7짹0.3 vs. 2.2짹0.4mm, and 2.3짹0.5 vs. 3.2짹0.6mm), respectively (p<0.01). Successful 4 PV isolations were achieved in all cases. Conclusions: AF ablation using CM mapping of only PVs, posterior LA wall and roof is time-saving method than whole LA mapping, and even more efficient merge around the PVs can be achieved.