Equilibria in aqueous solutions in the systems glycine + VO2+ and alanine + VO2+ have been studied by a combination of potentiometric and spectrophotometric methods, in the pH range 1.3-2.3 with high ligand-to-metal ratios. In this study an equilibrium model, MY, is assumed, where M and Y represent the metal ion and fully dissociated amino acid anion, respectively. The stability constants of these complexations and protonation constants of glycine and alanine are also given.