Objective of the study. To evaluate the effects of the purified micronized flavonoid fraction in the experimental models of various diseases of the venous system. Material and methods. The experiment was carried out on 140 Wistar rats allocated to 4 groups of 35 animals each. Group 1 contained animals with experimental deep vein thrombosis, group 2 was composed of the rats with model post-thrombotic disease,Group 3 was comprised of the animals with simulated — L-NAME-induced endothelial dysfunction, and group 4 — included the control animals. The purified micronized flavonoid fraction was applied at a daily dose of 100 mg/kg body weight during 6 months. Blood samples were taken at the scheduled time points for the measurement of the levels of biochemical markers of endothelial dysfunction. In addition, morphological investigations of the venous wall were conducted. Results. The application of  the purified micronized flavonoid fraction decreased the activity of lipid peroxidation and anti-oxidative enzymes (p<0.05). Simultaneously, it increased the nitric oxide (II) serum level but decreased activity of inducible nitric oxide (II) synthase (p<0.05). The animals of the model groups exhibited the enhancement of the reparative processes and the reduction of the severity of fibrous-sclerotic changes in the venous wall. Conclusion. The application of the purified micronized flavonoid fraction exerts the positive influence on the functional state of vascular endothelium and the morphological structure of the venous wall in experimental models of various diseases of the venous system.