Thermodynamic functions of complex formation of 15-crown-5 ether (15C5) with sodium cation (Na+) in the mixtures of water (W) with ethanol (EtOH) at different temperatures have been calculated. To obtain this function two experimental methods have been used. The equilibrium constants of complex formation have been determined by conductivity measurements and the enthalpic effect of complex formation has been measured by the calorimetric method and has been also calculated using van't Hoffs equation. The obtained results were compared and discussed. The complexes are enthalpy stabilized but entropy destabilized. (C) 2014 Elsevier B.V. All rights reserved.