The dissolution enthalpy of 1,4-dioxane and 12-crown-4 ethers in the mixture of water (W) and formamide (F) was measured at four temperatures: 293.15 K, 298.15 K, 303.15 K, 308.15 K. The standard molar enthalpy of solution, Delta H-sol degrees, depends on the size of cyclic ethers and on temperature. The values of Delta H-sol degrees become more negative with increasing molecule size and they increase in magnitude with increasing temperature. The effect of temperature on the process of preferential solvation of cyclic ethers has been discussed. (C) 2012 Elsevier B.V. All rights reserved.