Thermodynamic functions of complex formation of 15-crown-5 ether (15C5) with sodium cation (Na+) in the mixtures of water (W) with methanol (MeOH) at different temperature 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 Hoff's equation. The obtained results were compared and discussed. The complexes are enthalpy stabilized but entropy destabilized. (C) 2013 Elsevier Ltd. All rights reserved.