Background: Atrial fibrillation (AF) is a common cardiac arrhythmia, associated with increased cardiovascular morbidity and mortality including thromboembolic events. The aims of this study were to assess the prevalence of left atrial appendage (LAA) thrombi in Japanese non-valvular atrial fibrillation (NVAF) patients undergoing preprocedural transesophageal echocardiography (TEE) during anticoagulation therapy, and to compare the efficacy of warfarin and direct oral anticoagulants (DOAC). Methods and Results: This retrospective study reviewed records of 559 consecutive NVAF patients (445 men; age, 62 +/- 11 years) undergoing preprocedural TEE following at least 3 weeks of anticoagulation therapy. Of these, 275 patients had non-paroxysmal AF (49%). LAA thrombus was observed in 15 patients (2.7%). The prevalence of LAA thrombi was similar between the DOAC group (2.6%) and the warfarin group (2.8%, P=0.86). No patients with CHA(2)DS(2)-VASc score=0, or paroxysmal AF without prior stroke or transient ischemic attack, had LAA thrombi. On univariate analysis, non-paroxysmal AF, structural heart disease, antiplatelet therapy, larger left atrium, higher brain natriuretic peptide (BNP), reduced LAA flow, and higher CHA(2)DS(2)-VASc score were all associated with LAA thrombi. On multivariate analysis, BNP >= 173pg/mL remained the only independent predictor of LAA thrombi. Conclusions: LAA thrombi were found in 2.7% of Japanese NVAF patients scheduled for procedures despite ongoing oral anticoagulation therapy. Incidence of thrombi was similar for patients on DOAC and on warfarin.