The enthalpies of solution of solid Co(ClO4)2 . 6H2O and of water have been measured in binary mixtures of water with some alcohols (methanol, ethanol, 1-propanol and ethylene glycol) over the whole range of solvent composition. These data have been used for calculations of the enthalpies of transfer of Co(ClO4)2 from water to the mixtures. In the ethanol-rich mixtures, an alternative method of determining the enthalpies of transfer has also been applied. Electronic absorption spectra of ternary solutions of Co(ClO4)2 in mixed solvents have been measured as an aid in the interpretation of the calorimetric data.