The enthalpies of solution of benzo-15-crown-5 ether in ethanol + water and ethanol + water + sodium iodide systems have been measured at T = 298.15 K. The values of standard enthalpies of solution of benzo-15-crown-5 ether are positive in the mixtures of water and ethanol within the whole ranee of mixture composition. The equilibrium constants of complex formation of benzo-15-crown-5 ether with a sodium cation have been determined by conductivity measurements at T = 298.15 K. In the process of complex formation, ethanol molecules show their hydrophobic properties.