A modified UNIQUAC model was used to describe thermodynamic properties of binary water-carbohydrate mixtures. Interaction parameters are determined for glucose, fructose and sucrose. A new equation was developed to describe carbohydrate solubility in water from knowledge of dilution enthalpy rather than fusion enthalpy, and particularly when sugar crystallizes as a hydrated form. For all thermodynamic properties (water activity, osmotic coefficients, excess Gibbs energy, excess enthalpy, activity coefficients, boiling temperature, freezing temperature and solubility) the model agrees with experiments when reliable data are available. Good predictions are also obtained for water activity and osmotic coefficients in ternary systems (water-sucrose-glucose).