Despite the increased hypercoagulability of the blood plasma in patients with AF, the study of the processes of plasma hemostasis has still received insufficient attention, especially in patients with comorbid obesity or with excessive body weight. Purpose of the study. To establish the specific features of the effect of concomitant obesity on the indices of plasma hemostasis in patients with AF, on the basis of which to identify prognostically significant risk factors for adverse arrhythmia. Materials and methods. 75 patients with permanent AF were examined. For deducing prognostically significant risk factors, we conducted a retrospective analysis of the case histories of 421 inpatients. Results. The presence of concomitant obesity in patients with AF is accompanied by an acceleration of the prothrombinase-forming stage both in the internal and external hemocoagulation pathways. At the same time, the increase in procoagulant properties of blood is associated with a significant increase in fibrinogen and soluble fibrin-monomer complexes against the background of depletion of fibrinolytic and anticoagulant blood activity, which is a reflection of changes at the level of all links of hemocoagulation. Most diagnostically significant coagulation factors in the risk of thrombotic complications in patients with atrial fibrillation and concomitant obesity can be considered a measure of INR 30 minutes. Prognostically significant risk factors for small bleeding in patients with AF and associated obesity when taking warfarin are a BMI> 40kg/m 2 , level of AT III ≥40 % and ≥130 %, and in patients with AF and normal body weight, the amount of small bleeding increases if variability of INR beyond 2.0–3.0 and levels of AT III ≥130 %, as well as in the spring period of the year. Conclusions. Patients with AF are characterized by a moderate increase in the thrombogenic potential of the blood, which is accompanied by a significant inhibition of anticoagulant activity, while an increase in BMI leads to further deterioration of hemostasis equilibrium with an increase in procoagulant properties, depletion of fibrinolytic and anticoagulant blood activity.