Epidemiological surveys show that the incidence of atrial fibrillation has been increasing year by year, especially in the elderly, and the morbidity and mortality increase with age. Several clinical trials report that warfarin remains the main drug for the treatment of atrial fibrillation. The international normalized ratio (INR) is recommended as between 2.0 and 3.0 in European and American guidelines; however, there are racial differences between Asian and European and American populations. Warfarin anti-coagulation should be appropriately reduced, especially in the elderly patients with non-valvular atrial fibrillation who have high risks of stroke and bleeding. INR of 1.5-2.5 is safe and effective for them, which warrants a large number of clinical trials and evidence basis.