The reduction of graphite oxide makes it possible to obtain a graphene material with a developed surface, high conductivity and remarkable electrochemical behavior. The study of the electrochemical activity of oxygen-containing functional groups on the graphene surface is important for the creation of electrochemical energy sources and sensors. In this work, the reduced graphite oxide is selectively decorated by carboxyl functional groups. The initial and carboxylated reduced graphite oxide are studied by SEM microscopy, FTIR, Raman, and X-ray photoelectron spectroscopy. It is shown that a large number of carboxyl groups added to reduced graphite oxide surface change the sample morphology. Studying of reduced graphite oxide and carboxylated reduced graphite oxide by cyclic voltammetry shows reversible redox processes, which is associated with oxidation and reduction of the hydroxyl, carbonyl, and carboxyl groups. In addition, the dependence of peak potentials on the pH value is studied.