Objective. To analyze the features of multiple sclerosis (MS) pathological progression by the parameters of oxidative stress and antioxidant defense system (ADS). Material and methods. The study included 220 patients with different clinical forms and phases of MS who were examined and divided into four clinical groups. The intensity of lipid and protein free-radical oxidation (FRO) was evaluated by the level of ketodienes, diene conjugates, malondialdehyde, and Schiff bases. The functioning of the endogenous AFS was assessed by activity of the following markers: vitamin E, general and non-protein SH-groups, which represented the nonenzymatic AFS segment. The enzymatic segment markers were superoxide dismutase, glutathione peroxidase, and glutathione reductase. Results and сonclusion. Significant differences in the oxidative stress intensity in patients with different clinical forms and phases of MS were revealed. The results have made it possible not only to identify oxidative stress in the MS course in the evidence-based practice but also to confirm the continuity of pathological process of this disease.