A negative impact of radicals on human’s health is responsible for growing research interest in antioxidant properties of substances, which protect organisms from the damaging influence of these reactive species. Angiotensin-converting enzyme inhibitors (ACE-I) are the most popular drugs used in cardiovascular diseases. There are a lot of clinical reports that ACE-I have antioxidant properties, due to the fact, that prolonged use improves conditions of patients with neurodegenerative disorders and slow inflammatory processes. The paper shows the antioxidant properties of a selected ACE-I: cilazapril, ramipril, imidapril, lisinopril, perindopril, and quinapril. Among numerous methods for antioxidant activity estimation, DPPH reduction is the most popular and commonly used one due to its ease, speed, sensitivity and the usage of stable radicals. UV-Vis spectrophotometry was used to examine interactions of chosen ACE-I with model-free radicals. Absorption of UV-Vis spectra of DPPH (reference), and DPPH interacting with the tested ACE-I were compared. For all tested ACE-I kinetics of their interaction with DPPH, up to 30 minutes, were obtained. The strongest interaction with DPPH was observed for imidapril and cilazapril and the lowest interaction for lisinopril. Studies have shown usefulness UV-Vis spectrophotometry for obtaining information on interactions of ACE-I with model-free radicals.