Background: Warfarin reduces the risk of stroke in patients with atrial fibrillation (AF) but is often underused in clinical practice. We aimed to examine the current state of warfarin use in nonvalvular atrial fibrillation (NVAF) patients with first-ever ischemic stroke (IS) or transient ischemic attack (TIA) in China and to analysis factors causing such underuse. Methods: By accessing the China National Stroke Registry, data on consecutive patients with known NVAF who developed first-ever IS or TIA were studied. Proportion of warfarin use was estimated in those patients with known NVAF who should be eligible for anticoagulation therapy. Factors associated with warfarin underuse were identified by multivariate logistic regression. Results: Of 11,080 patients with first-ever IS or TIA, 996 (9.7%) had NVAF and no contraindications to anticoagulation therapy and 592 of them had history of AF. Among these patients, only 96 (16.2%) were on warfarin and 496 (83.8%) were not. In those patients on warfarin, only 1 of his international normalized ratios on admission was in the therapeutic range of 2.0-3.0. Based on the CHADS(2) scores, about 20.2% low-risk AF patients took warfarin; however, only 15.2% moderate and 16.4% high-risk patients were on warfarin. Older patients and patients with history of coronary heart disease (CHD) were less likely to be given warfarin, whereas patients with history of prestroke antiplatelet use were more likely to take warfarin. Conclusions: We found that warfarin was significantly underused in patients with known NVAF in China. Age and CHD and prestroke antiplatelet therapy were related factors.