Radiosensitizers are drugs that make cancer cells more sensitive to radiation therapy. The cytotoxic properties of such compounds are due to the fact that in the cell these compounds undergo one-electron reduction to generate radical anions. Therefore, their theoretical and/or experimental study is of high interest. To determine the correlation between reduction potential determined by cyclic voltammetry measurements and some physicochemical properties of selected radiosensitizers theoretical calculations of electron affinities based on the DFT method with B3LYP functional at the level of 6-311++G** basis set in vacuum were utilized. Very good correlation was found between electron affinities of radiosensitizers and their reduction potential and so called E71 potential that account for the energy necessary to transfer the first electron to an electroactive group at pH 7 in aqueous medium to form a radical anion.