The S-UNIFAC model of Spiliotis and Tassios (Fluid Phase Equilib. 2000, 173, 39), developed for systems containing sugars, is modified here by replacing the LLE-UNIFAC model with the modified UNIFAC model of Larsen et al. (Ind. Eng. Chem. Res. 1987, 26, 22 74). This modification was motivated after an extensive evaluation-especially in systems containing molecules that differ significantly in size (asymmetric systems) such as those considered here-of the commonly used UNIFAC models. The applicability of the new model, called modified S-UNIFAC (mS-UNIFAC), is extended, as compared to S-UNIFAC, to mixtures of sugars with acids and esters and to mixtures containing sugar derivatives, such as sugar esters. Through the use of a better combinatorial term and new data, the model becomes more reliable than S-UNIFAC, providing satisfactory predictions for multicomponent systems involved in the enzymatic esterification reactions for the production of fatty acid sugar esters, for which S-UNIFAC fails.