Abstract: Objective：To assess the value of two-dimensional (2D) transesophageal echocardiography (TEE) and real-time three-dimensional (3D) TEE in left atrial appendage closure (LAAC). Methods：Both 2D-TEE and real-time 3D-TEE were performed in forty-six patients with nonvalvular atrial fibrillation (CHA2DS2-VASc ≥ 2). The internal diameter, depth, and lobulation of the left atrial appendage (LAA) detected with the two methods were recorded, and then compared with those detected with angiography. And the correlation between these parameters and the size of the occluder implanted were evaluated. Results：Forty-six patients underwent LAAC under TEE monitoring. The maximum internal diameters of LAA detected with 3D-TEE, 2D-TEE, and angiography were (22.73±3.80) mm, (21.45±4.01) mm, and (23.15±4.17) mm, respectively. There was no statistically significant difference among the 3 methods. The maximum internal diameters of LAA measured with 3D-TEE or angiography were more closely correlated with the size of the occluder implanted than that detected with 2D-TEE (3D-TEE: r=0.907, 95% CI 0.837-0.948，P<0.001; 2D-TEE: r=0.770，95%CI 0.617-0.866, P<0.001; angiography: r=0.808, 95%CI 0.676-0.889, P<0.001). Conclusions：3D-TEE combined with angiography can be used to accurately measure the internal diameter of LAA and might play an important role in the procedure of LAAC.