Background It has not been clearly demonstrated whether the pattern of Complex Fractionated Atrial Electrogram(CFAEs) during atrial fibrillation(AF) is related to electro-anatomical remodeling and left atrial(LA) volume of the LA. Methods and Results 100 patients (83males, 55.0짹10.6 years old) with AF (51 paroxysmal AF (PAF), 49 persistent AF (PeAF)) who underwent RFCA guided by computed tomography (CT) merged NavX map were included. We evaluated color coded CFAE map and voltage maps acquired during high right atrial pacing (pacing cycle length 500ms) and AF. The regional CFAE-cycle length (CL) and LA voltages during pacing (VolPACE) and AF (VolAF) were compared in patients with LA volume ���125mL (n=49) and those <125mL (n=51). Results: 1. Mean VolPACE was significantly lower (p=0.0047) in patients with LA ���125mL than those <125mL. This difference was consistent in venous atrium (VA; p=0.0038), Anterior LA (ALA; p=0.0407) and LA appendage (LAA; p=0.0075). 2. Mean CFAE-CL (p=0.0030) was longer in patients with LA ���125mL than those <125mL. This difference was also consistent in LAA (p=0.0174), VA (p=0.0160), ALA (p=0.0034), Left lateral isthmus area (LLI; p=0.0102). 3. The CFAE area (CFAE-CL<120 ms) were predominantly located in septum (38.8% vs. 54.9%), roof (18.4% vs. 47.1%), and LAA (42.9% vs. 52.9%) in both groups. The proportion of CFAE area to total LA surface in patients with LA ���125mL was significantly smaller in those <125 mL (p=0.0058). Conclusion In patients with electroanatomically remodeled LA, proportion of CFAE area was smaller and regional CFAE-CL was longer than those with normal LA sized patients with AF. The patterns of CFAE were closely related to the degree of electro-anatomical remodeling of the LA.