Abstract <p>Kinetic regularities of hydroxychloroquine sulfate (HCQ) degradation in an aqueous medium during UV radiation and also in the presence of an oxidizer in the UV/HCQ/H₂O₂ system and a catalyst in the photo-Fenton system are established. The degree of degradation for 1 h of irradiation is found to reach up to 50.4% in the dependence on the concentration prepared. The kinetics of HCQ degradation follows the kinetics of pseudo-monomolecular reaction. The calculated reaction rate constants vary in the range of (0.4‒8.4) × 10^–3 min^–1. The degree of drug degradation in the presence of H₂O₂ reaches 78.9% at optimal conditions ([Н₂О₂] = 85 mg/L, <i>t</i> = 25°C, λ = 220 nm, pH = 4.5). During the degradation in the photo-Fenton system, the dependence of the reaction rate on molar [H₂O₂]/[Fe²⁺] ratio is also studied. The study revealed that, in the concentration range ([Fe²⁺] = 0.28–1.12 mg/L, [H₂O₂] = 85 mg/L, <i>t</i> = 25°C, λ = 220&#xa0;nm, the optimal [H₂O₂]/[Fe²⁺] ratio = 80 at pH = 4.5, and the degree of hydroxychloroquine sulfate degradation in the photo-Fenton system is 86.1%. The apparent reaction rate constants calculated at various [H₂O₂]/[Fe²⁺] ratios from 1 : 50 to 1 : 200 have values in the range of (4.1–5.5) × 10^–2 min^–1.</p>