Aim. The comparative assessment of the effectiveness of thrombolysis with the use of encapsulated (streptokinase-containing pectinate and liposomal nanoparticles) and non-encapsulated streptokinase in experiment. Material and methods. Experimental design: Liposomal, pectinate, and non-encapsulated forms of streptokinase were systemically administered to 30 male rats with experimental venous thrombosis. The animals were divided into three groups each comprised of 10 rats. The control group also contained 10 rats. Thrombosed veins for immunohistological studies were harvested 1.5 hours after streptokinase administration. The main criteria for its effectiveness included the intensity of thrombolysis evaluated based on the results of light microscopy and thrombolysis coefficient in  conjunction with endothelial injury and dysfunction assessed from Willebrand factor expression in endotheliocytes in response to different forms of streptokinase. Results. Administration of liposomal streptokinase as a thrombolytic agent resulted in complete lysis of the fibrinic component of the thrombus in 80% of the observations whereas these fibrin fragments were preserved in 100% of the animals treated by the administration of pectinate and native forms of streptokinase (thrombolysis coefficients 0.5, 1.03, and 0.7 respectively). Encapsulated forms of streptokinase, unlike non-encapsulated ones, caused weak or moderate staining of endothelial cell cytoplasm with anti-Willebrand factor antibodies in the rat veins. Conclusion. Thrombolysis in the veins of experimental animals occurred within 1.5 hours after the administration of the  encapsulated and non-encapsulated forms of streptokinase. The best results were obtained using the encapsulated liposomal form of streptokinase. Pectinate and liposomal nano-containers protected vascular intima against the injurious action of streptokinase.