Background: Left atrial appendage (LAA) is an important source of thromboembolism and stroke in patients with atrial fibrillation (AF). However, the relationships between LAA and stroke have not been systematically investigated. This study evaluated the features of LAA associated with stroke in patients with AF. Methods: We enrolled 224 nonvalvular AF patients with non-hemorrhagic stroke (Group 1, 71 women, age 67.3 짹 10.1 years). Control group included 365 patients with nonvalvular AF (Group 2, 77 women, age 55.7 짹 11.1 years), who underwent computed tomography (CT) during the same period. The orifice size (the longest x shortest diameter) and the depth of LAA were measured using CT. Results: Group 1 included more female patients (31.7% vs. 21.1%, p=0.004), and was older than group 2 (p<0.001). There was no difference in the incidence of persistent AF between two groups (p= 0.97). CHADS2 score (3.2 짹 0.8, vs. 0.6 짹 0.7, p<0.001) and LA dimension (4.76 짹 0.82 vs. 4.12 짹 0.59 cm, p<0.001) were significantly lager in group 1 than in group 2. The orifice size (3.85 짹 1.66 vs. 2.57 짹 0.93 cm2, p<0.001) and depth of LAA (3.18 짹 0.67 vs. 2.67 짹 0.57 cm, p<0.001) were significantly larger in group 1 than group 2. In multivariate analysis, age (OR 2.08 per decade increase, 95% CI 1.59-2.71, p<0.001), LA size (OR 1.89, 95% CI 1.29-2.76, p=0.001), the orifice size (OR 1.58, 95% CI 1.26-1.99, p<0.001) and the depth of LAA (OR 1.91, 95% CI 1.24-2.95, p=0.004) were independent predictors of stroke. In the receiver operating characteristic curve (ROC) analysis, the orifice size of LAA showed the largest area under the ROC curve of 0.771 and a value of > 3.0 cm2 predicted stroke with sensitivity of 71% and specificity of 70%. Conclusion: In patients with non-valvular atrial fibrillation, the larger orifice size and depth of LAA were independent predictors of stroke with advanced age and LA enlargement.