Anticoagulant therapy is an effective stroke prevention measurement for subjects with atrial fibrillation (AF) who are at high risk of ischemic stroke. However, it is reported that oral anticoagulants (OACs) are generally underused in clinical practice. A better awareness of current usage of anticoagulant therapy would enable prevention of stroke secondary to AF. Therefore, we determined the nationwide prevalence of AF and the frequency of OACs use among patients with ischemic stroke in China. Based on the China National Stroke Screening Survey, a representative nationwide sample of 1,252,703 adults over 40 years old during 2013 and 2014 was involved. Information on demographic data, diagnosis of stroke, behavioral risk factors, family history of stroke, related diseases, and medications was collected. The community-based survey data showed that 5,588 patients (12.0%) with ischemic stroke had previous, or newly diagnosed, AF. Therefore, more than 2.15 million ischemic stroke patients had AF in China. Among ischemic stroke patients with AF, the strongest risk factor was coronary heart disease (odds ratio = 2.53), whereas dyslipidemia accounted for the largest contribution (population-attributable risk proportion = 17.33%). Of ischemic stroke patients with AF, only 2.2% had taken OACs; of them, 98.2% had taken warfarin. In conclusion, a large number of ischemic stroke patients with AF are significantly undertreated with OACs in China. This highlights the need for improvement of prevention of ischemic stroke secondary to AF.