Functionalized polymers are widely applied in the biomedical field as tools in diagnosis and treatment of diseases [1]. Polymer particles can be adsorbed or loaded with multiple drugs and can more effectively control drug release in the body. Chitosan is a natural polymer that is abundant in nature. Due to its good physico-chemical properties and unique biological properties, chitosan is applied in many industries [2]. Polyphenols are well known for their antioxidant properties, they are natural compounds with one or more phenolic groups. They have a major influence on many diseases [3].The functionalisation of maleic anhydride to chitosan was performed in the first step according to the scheme presented in Figure 1.formulaFig. 1. The reaction mechanism of chitosan grafting to copolymer I After purification of copolymer I by sedimentation, it was added in the dimethylformamide, subjected to quercetin grafting according to the scheme presented in Figure 2.formulaFig. 2. The reaction mechanism of chitosan grafting to copolymer II The chitosan-quercetin copolymer was synthesized by chitosan functionalization in the first step with maleic anhydride, then in step II the copolymer I was treated with ethyl chloroformate and triethylamine, after which in step III the obtained copolymer II was functionalized with quercetin. At every step for all copolymers the IR spectra were obtained. Was determined antioxidant activity by the ABTS and DPPH methods. It was found thatchitosane functionalized with quercetin has stronger antioxidant activity than thepure quercetin of the same concentration.