Complex [(O)V^IV(C₂O₄)(Phen)(H₂O)] was obtained on the basis of V₂O₅ and malic acid in the presence of concentrated HNO₃ and phenanthroline. Its structure was determined by the X-ray structural analysis; its magnetic susceptibility was measured. The role of the VO2+ and VO²⁺ cations in the oxidation and complex-formation processes was considered. A method for the conversion of malic acid to oxalate anions through the formation of oxaloacetic acid and the intermediate products of its decarboxylation reactions was proposed. It was shown by the DFT M06/6-31G(d,p) method that the transition state energy decreases in the way of the HOC(O)C(0)CH₂-COOH bond breakage during decarboxylation compared with the free acid in the intermediate of its anion with VO²⁺.