Introduction Left atrial (LA) CFAE (complex fractionated atrial electrograms) during atrial fibrillation (AF) has been demonstrated as an effective guide for the catheter-based substrate modification in patients with chronic, longstanding AF (CAF). However, the role of right atrial (RA) CFAE is debating whether the ablation guided RA CFAE is beneficial or not. The aim of this study was to clarify the characteristics of RA CFAE and their clinical value in the catheter ablation of CAF. Methods Twenty patients with long lasting CAF who failed to AF termination or conversion from AF to atrial tachyarrhythmias (ATs) after pulmonary vein isolation (PVI) and LA CFAE ablation were included. CFAE was identified by 3-D automated mapping (NavX. ver 8.0) system. Results The distribution of RA CFAE area was shown in Figure 1. The conversion form AF to ATs was observed in 13 (65%) of 20 patients during ablation. Of 13 patients, this conversion point was observed at the CT (n=3), high septum (n=3), sinus venosus (SV, n=1), RAA (n=1), CS os (n=1), low posterior (n=1), superior vena cava (SVC, n=1). In the remaining 3 patients who took LA CFAE ablation again after RA CFAE ablation, the conversion point was observed at perimitral isthmus (n=2) and LA appendage (n=1). Seven out of 13 ATs terminated by mapping-guided ablation, of which critical sites were cavotricuspid isthmus (n=3), high septum (n=2), SV (n=1) and LA appendage (n=1). AF directly converted to SR during ablation at the SVC in 1 patient and CS os in 1. Conclusion RA CFAE is clustered at the specific anatomical structures, such as RAA, CT and high septum. RA CFAE ablation is effective in termination of AF or elimination of secondary ATs in whom AF was not terminated after PVI and CFAE guided extensive LA ablation.