Given that oxidative stress represents an important etiological factor in the pathogenesis of psoriasis, the aim of this study was to assess the effects of different therapeutic approaches, methotrexate, secukinumab, and ustekinumab on systemic oxidative stress biomarkers in psoriatic patients. This study involved 78 psoriatic patients, divided into the group treated with methotrexate (23 patients), secukinumab (28 patients), and ustekinumab (27 patients), and 15 healthy controls. Oxidative stress biomarkers (index of lipid peroxidation measured as TBARS, nitrites (NO), superoxide anion radical (O), and hydrogen peroxide (HO)) and antioxidative defense system (superoxide dismutase (SOD) activity, catalase (CAT) activity, and reduced glutathione (GSH)) were determined spectrophotometrically from the blood before the initiation of therapy in 16th, 28th, and 52nd week. O and SOD showed the most prominent changes comparing the psoriatic patients and healthy controls. CAT activity was significantly lower in psoriatic patients, and methotrexate induced a further decline in CAT activity. Ustekinumab induced a significant increase in GSH level after 52 weeks of treatment, while methotrexate reduced GSH. All applied therapeutic options induced a reduction in PASI, BSA, DLQI, and EARP. Biological drugs exert more pronounced antioxidant effects compared to methotrexate, which is most clearly observed in the values of O and SOD.