Modification the biodegradable matrix was carried by graft-copolymerization polylactide with methacrylic acid of various concentrations. Ultraviolet irradiation with different exposure times to the samples was chosen as the initiator of copolymerization. In the experiment the effect of ultraviolet light on polylactide and graft copolymerization was investigated: the resulting samples were studied by viscosimetry, gravimetry, FTIR, static cation- exchange capacity analysis . The conditions for obtaining grafted copolymers and the dependence of the characteristics on the reaction conditions are established.