The mechanism and efficiency of mass transfer in two-phase liquid-liquid systems are investigated. Experiments were carried out in a high-shear in-line rotor-stator mixer. The method applied is based on the experimental determination of both the product distribution of the chemical test reactions and the drop size distributions. The product distribution of the complex test reactions was determined based on high-performance liquid chromatography measurements. The drop size distribution was measured just after the process. The multifractal model of drop breakage and the model of mass transfer by Favelukis and Lavrenteva were applied to identify the energetic efficiency of drop breakage and mass transfer in the in-line rotor-stator mixer.