In the present study the potential of two thermodynamic-based models (the group-contribution UNIFAC model and the a priori predictive COSMO-RS model) to predict solute partitioning in aqueous surfactant solutions is evaluated. In order to take into account the small size of micelles, the UNIFAC model was extended by the interfacial contribution based on the Gibbs-Thompson equation. The applicability of the approach was successfully proved for the partitioning of nonpolar solutes (toluene, p-xylene) in aqueous solutions of nonionic surfactants. The original COSMO-RS model underestimates the concentration of the solute in the aqueous phase in the case of micellar systems since it does not account for the small size of micelles. At the same time, this model gives quantitative results for the octanol/water partition coefficients of both solutes under study leading to the conclusion that the affinity of both solutes to a certain solvent is well described. Thus, extending the COSMO-RS by the interfacial term seems to be promising.