Thermodynamics of single-phase complex systems of glucose + alcohol + water is significantly important in food and pharmaceutical industries. The water activity is a practical parameter in thermodynamic characterization in food and pharmaceutical and other biological industries, which its value has an important role in growing microorganisms and rate of reactions. In this work, the NRTL-NRF excess Gibbs function has extended for ternary system of water, different alcohols (as second molecular solvent) and a special molecular solute like a sugar. The extended NRTL-NRF model with three parameters was Used for correlation of the osmotic coefficient of the aqueous systems of glucose and alcohol at different concentrations. The data of the osmotic coefficient of water for these systems are obtained by an isopiestic method. The adjustable parameters are calculated by optimization of the experimental data of the osmotic coefficient using the Nedler-Mead algorithm. It is shown that the results of the modified NRTL-NRF model demonstrate low deviation from the experimental data. (c) 2008 Elsevier B.V. All rights reserved.