The transfer energies of hydrochloric acid in ethyl urea + water mixtures have been determined from electromotive force measurements of cells consisting of hydrogen and silver-silver chloride electrodes immersed in the mixed solvents containing the acid. Four different ethyl urea (EU) + water mixtures, involving 11.52, 20.31, 29.64 and 36.83 percentages by weight of EU, have been used. The molal concentration of the HCl solutions varied from 0.02 to 0.2 mole/kg with respect to each solvent composition. The effect of temperature on the behavior of the system was also studied by measuring the cell potential at five different temperatures between 278.15 and 318.15 K. The free energy of HCl transfer decreased steadily with increasing the EU content of the mixed solvent. The entropy (T?S°i) and enthalpy (?H°i) of transfer increased rapidly to maximum values and then decreased as the mole fraction of EU in the mixture increased. The increase in T?S°i and ?H°i was ascribed to the formation of hydrogen bonded EU + water complexes that are solvating the transferred ions. The structure enhancement in the mixed solvent was found to be more pronounced as compared with such mixed solvents as aqueous urea or methyl urea