The micelle-water partition coefficient K-MW is measured for itaconic acid and some of its esters for micellar solutions of the surfactants sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and t-octylphenoxypolyethoxyethanol (Triton X-100). Additionally, K-MW is predicted using the conductor-like screening model for real solvents (COSMO-RS) and calculated from log K-MW-log K-OW relations. We find that, because of the increasing length of the alkyl chain in the ester, K-MW increases, and the COSMO-RS predicted values agree well with the experimental ones. Furthermore, COSMO-RS is used to screen the partitioning of the esters in micellar solutions of a homologous series of surfactants (NaCnS, n = 8-16). For hydrophobic solutes, we predicted an increase in K-MW with increasing n, while for less hydrophobic solutes, K-MW is constant.