BACKGROUND A specific morphology of left atrial appendage (LAA) has been reported to be related to stroke in nonvalvular atrial fibrillation (AF) patients. However, the mechanism is not completely understood. This study evaluated whether a specific LAA morphology was related to stroke, and whether it was related to the change of flow velocity and size of LAA in AF patients. METHODS The morphology, size, and flow velocity of LAA were evaluated in AF patients with ischemic strokes (stroke, n = 160) and age-matched AF patients without ischemic strokes (control, n = 200). RESULTS Compared with control, the stroke group had a larger LA dimension (4.5 ± 0.7 vs. 4.2 ± 0.6 cm, P < 0.001), larger LAA orifice area (5.3 ± 2.1 vs. 4.1 ± 1.7 cm2 , P < 0.001), and slower LAA flow velocity (37 ± 19 vs. 51 ± 20 cm/s, P < 0.001). The stroke group had the chicken wing type less frequently than the control (34% vs. 50%, P = 0.003). After an adjustment for multiple potential confounding factors, the chicken wing type LAA had a decreased stroke risk (odds ratio 0.34, 95% confidence interval 0.14-0.84, P = 0.020). Patients with a chicken wing LAA had a smaller LAA orifice area (4.4 ± 1.6 vs. 4.9 ± 2.2 cm2 , P = 0.013) and higher LAA velocity (55 ± 19 vs. 41 ± 20 cm/s, P < 0.001) than those with non-chicken wing LAA. CONCLUSIONS A chicken wing type of LAA was related to the less incidence of stroke. Our results suggest that the relationship between a specific LAA morphology and stroke might be partially explained by the change of the size and flow velocity of LAA.