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Abstract: In this work, the interfacial mass transfer in two extraction systems, namely acetone-toluene-water (System I) and hexane-heptane-methanol (System II), was examined experimentally and theoretically. The interfacial mass transfer was experimentally examined by using a Nitsch-Cell. As theoretical approach the density gradient theory (DGT) in combination with the Koningveld-Kleintjens (KK) model was used. At first, the KK-model was used to model the liquid-liquid equilibrium of System I and System II. In combination of the KK-model with the DGT, the interfacial tension was modelled by fitting the influence parameter of the DGT. To estimate the required mutual mobility coefficients in each system, bulk diffusion coefficient coefficients were used. It was shown, that the DGT in combination with a thermodynamic model and experimental information of the bulk diffusion coefficients and the system’s interfacial tension is able to model the interfacial mass transfer. Moreover, it can be stated that the DGT predicts a high enrichment of acetone in System I and this enrichment has an influence on the mass transfer.