Abstract. In this work, the synthesis of iron ( Fe(II)), cobalt (Co(II)) and zinc (Zn(II)) ion complexes with flavonoids quercetin and rutin was studied , and their stability constants at different pH values were estimated. The synthesis of the complexes was carried out under spectrophotometric control , and the stability constants were determined by the isomolar series method. The results showed that the stability of the complexes depends on the acidity of the medium, with the highest values of the stability constants being recorded for quercetin complexes with Fe(II) at neutral pH. The data obtained indicate the prospects for using these complexes in medicine and agricultural technology, in particular for targeted drug delivery and antioxidant therapy.