This article studies in detail the process of complex formation of quercetin with cobalt(II) ions and the spectral properties of the resulting compound. The complex was synthesized in aqueous solutions, and the characteristics of the resulting compound were studied using UV and infrared spectroscopy. The shift of the absorption maximum of quercetin in the UV spectra and the appearance of new absorption lines confirm the formation of the complex. The infrared spectra recorded changes in the vibrations of the functional groups involved in the coordination reaction in the quercetin molecule. The results of this study expand the existing knowledge on the properties of metal complexes with flavonoids and open new perspectives for their biological and chemical applications. Synthesis and physicochemical characterization of cobalt(II)-quercetin complexes Cobalt(II) ions formed complexes with quercetin in different stoichiometric ratios. The optimal conditions were determined and the stable form of the complex was observed at the cobalt(II): quercetin ratio of 1:2.