Backgrounds: Although multislice computed tomography (MSCT) provides precise measurement of cardiac chamber size and volume using the 3-dimensional reconstruction, it is practically not suitable to use MSCT for serial monitoring due to the hazards of radiation exposure. The aim of this study was to evaluate the feasibility and reliability of echocardiographic measurement of left atrial (LA) volume and function. Methods and Results: Echocardiography and MSCT were conducted in patients with paroxysmal atrial fibrillation (PAF, n=33) and non-paroxysmal AF (non-PAF, n=24) undergoing catheter ablation. LA volume (LAV) was measured with standard method by MSCT, and modified Simpson���s method and area-length method by echocardiography. With echocardiographic method, estimated LAV can be easily calculated from 2 manually traced areas and 2 orthogonal LA dimensions. In patients with PAF, LAV and LAEFTotal using MSCT were significantly correlated with those by echocardiography: LAVMax: 121.9짹46.8 ml vs. 80.7짹32.0 ml (r=0.596, p=0.025), LAVmin: 81.5짹41.8 ml vs. 44.2짹28.4 ml (r=0.908, p<0.001), LAEFTotal: 34.9짹14.9 % vs. 48.6짹13.7 %, (r=0.876, p<0.001). In patients with non-PAF, LAV and LAEFTotal using MSCT were also closely correlated with those by echocardiography: LAVMax: 138.8짹45.0 ml vs. 84.7짹23.9 ml (r=0.700, p=0.036), LAVmin: 107.3짹49.6 ml vs. 50.2짹25.7 ml (r=0.800, p=0.010), LAEFTotal: 26.0짹12.0 % vs. 43.5짹17.2 %, (r=0.795, p=0.010). However, compared to MSCT, measurement by echocardiogaphy resulted in a significantly smaller LAV, with a mean underestimation of LAV of 48% Conclusion: Although echocardiography underestimates LAV by approximately 48%, LAV and LAEF measured by echocardiography showed good correlations with those by standard method using MSCT. Echocardiography is convenient and reliable modality to estimate LAV and function irrespective of type of AF.