Introduction. Chronic venous insufficiency (CVI) of the lower extremities remains a widespread condition characterized by inflammation, endothelial dysfunction, and activation of hemostasis. Current evidence indicates the formation of a persistent prothrombotic microenvironment that contributes to disease progression. Against the background of growing interest in complementary nutraceuticals, fucoidans—sulfated polysaccharides derived from brown seaweed – have attracted particular attention due to their anticoagulant, anti-inflammatory, and profibrinolytic properties. However, clinical data on the safety and efficacy of nutraceutical use in patients with CVI remain limited. Aim of the study: to evaluate the efficacy and safety of prophylactic intake of a fucoidan-containing Proresilient supplement in patients with chronic venous insufficiency. Materials and Methods. A prospective observational comparative study was conducted involving 40 patients with chronic venous insufficiency, randomized into the main group (standard therapy plus a fucoidan-containing Proresilient supplement) and the control group (standard therapy alone). The course of the fucoidan-containing nutraceutical lasted 30 days. The primary efficacy parameters were the international normalized ratio (INR) and activated partial thromboplastin time (APTT); secondary parameters included prothrombin time, prothrombin activity (Quick), thrombin time, fibrinogen, D-dimer levels, leukocyte and neutrophil counts, and ESR. Statistical significance of changes over time was determined at p