A new approach is proposed by introducing mixture-type groups to the modified universal functional activity coefficient (UNIFAC, Dortmund) model for prediction of infinite dilution activity coefficients in highly nonideal aqueous solutions. The mixture-type group means a hypothetical one that appears in a particular type of mixtures only, and is considered here to account for hydrophobic effects specially taking place in a type of systems including water. Compared with the analytical solution of group (ASOG) model, the various UNIFAC models, and the correlation method of Pierotti, Deal and Derr (PDD), the new method has shown good accuracy. In addition, the new method can also improve considerably the predictive accuracy of mutual solubility, especially for systems with very small distribution ratios, in such cases the present group contribution models with common interaction parameters perform unsatisfactorily.