Left atrial appendage (LAA) evaluation is important to select the optimal LAA closure device for patients with atrial fibrillation (AF). The LAA characteristics of Japanese patients remain uninvestigated. We compared the LAA size and morphology between 212 Japanese AF patients before catheter ablation and 119 AF patients undergoing LAA closure in the United States (US). We measured the LAA ostial dimension and depth by transesophageal echocardiography in all patients and determined the LAA morphology types of Japanese patients by multidetector cardiac computed tomography and those of US patients by LAA angiography. The maximum LAA ostial dimension was significantly larger in Japanese patients than in US patients (22.6 ± 4.1 mm vs. 21.5 ± 3.5 mm, P = 0.02). Also, Japanese patients had larger maximum dimension and depth corrected by body surface area than US patients in both paroxysmal and nonparoxysmal AF groups. The angle showing the maximum dimension was 0° or 135° in approximately 75% of patients in both groups. The common LAA morphology types were “cauliflower” and “chicken wing” in Japanese patients and “cactus” and “windsock” in US patients. In this study, Japanese patients had a larger LAA size than US patients. Because the maximum LAA dimension was obtained at the same angles, the LAA measurement method for US patients can be applicable to Japanese patients.