The reverse micelle (RM) media are very good as nanoreactors because they can create a unique microenvironment for carrying out a variety of chemical and :biochemical reactions. The aim of the present work is to determine the influence of different water-dimethyl sulfoxide (DMSO) mixtures encapsulated in 1,4-bis-2-ethylhexylsulfosuccinate (AOT)/n-heptane RMs on the enzymatic hydrolysis of N-benzul-L-tyrosine (Bz-Try-pNA) by alpha-chymotrypsin (alpha-CT). The reaction was first studied in homogeneous media at different DMSO-wafer mixture compositions and in DMSO-water/AOT/n-heptane RMs. The hydrolysis rates of Bz-Try-pNA catalyzed by alpha-CT were determined by UV-vis spectroscopy. The reaction follows the Michaelis-Menten mechanism and the kinetic parameters: k(cat), K-M, and k(cat)/K-M were evaluated under different conditions. In this homogeneous media, DMSO plays an important role in the solubilization process of the peptide which is almost insoluble in water, but it has a tremendous impact on the inactivation of alpha-CT. It is shown that the enzyme dissolved in a 20% molar ratio of the DMSO-water mixture does not present enzymatic activity. Dynamic light scattering, has been used to assess the formation of DMSO-water/AOT/heptane RMs at different DMSO, compositions. The results also, show that there is preferential solvation of the AOT RM interface by water:, Molecules. To test the use of these RMs as nanoreactors, the kinetic parameters for the enzymatic reaction : in these systems have been evaluated. The parameters were determined at fixed W-S {W-S = ([water] + [DMSO])/[AOT] = 20} at different DMSO-Water compositions. The results show that the Michaelis-Menten mechanism is valid for alpha-CT in all the RM systems studied and that the reaction takes place at the RM interface. Surprisingly, it was observed that the enzyme encapsulated by the RMs show Catalytic effects with similar k(cat)/K-M values at any DMSO composition investigated, which evidence that DMSO molecules are localized far from the RM interface.