The stability constants of Cu(SCN)+ in the Cu(SCN)+-NaNO3-C2H5OH-H2O system were determine by spectrophotometric measurements at 25?for 0, 5, 10, 15, 20 and 25 wt.% alcohol in mixed solvents. The total ionic strength of the solution is 0.2-2.0 mol.dm-3, and pH = 1.5-1.6. On the basis of Pitzer's theory, a method of determing thermodn. stability constants of coordination compounds in mixed solvents by curve fitting technique is proposed. The stability constants of Cu(SCN)+ in mixed solvents are correlated with composition and dielec. constant of the solvent mixture

Key words: ETHANOL, WATER, ACTIVITY COEFFICIENT, MEDIA, STABILITY CONSTANT, THIOCYANATE, COPPER COMPLEX, ELECTROLYTE, QUATERNARY SYSTEM, SODIUM NITRATE