<p>The reactions giving single- and mixed-ligand coordination compounds in ternary systems containing copper(<span>ii</span>) cations, tris(hydroxymethyl)aminomethane, and polyamines (ethylenediamine, diethylenetriamine, or triethylenetetramine) were studied in aqueous solutions by spectrophotometry. By changing the component composition of solutions of ternary systems, the optimal conditions were found for the formation of coordination species, and their composition was determined from the electronic absorption spectra. In alkaline solutions of the ternary copper(<span>ii</span>)—tris(hydroxymethyl)aminomethane—ethylenediamine system, the formation of a mixed-ligand complex with an equimolar composition of the coordination sphere was confirmed, for which logβ is 12.83±0.24. For the ternary copper(<span>ii</span>)—tris(hydroxymethyl)aminomethane—tdiethylenetriamine or triethylenetetramine systems, the preferential coordination of polyamines, in which the complexing properties of the aminohydroxyl ligand are blocked, was established.</p>