The anomalous characteristics of the enzymatic reactions in water-in-oil microemulsions (reverse micelles (RMs)) of ionic surfactants are sought to be explained in light of the electrical double layer theory. The characteristics investigated are (1) the enhanced activity in the reverse micellar solutions as compared to that in the bulk aqueous solution (defined as an aqueous solution whose substrate concentration equals the overall concentration [S 0] ov in the entire micellar system); (2) the bell-shaped dependence of the activity on the hydration ratio ( W 0); and (3) the shifts in the enzymatic activity vs the stock solution pH for different hydration ratios with respect to the enzymatic activity shifts in the bulk aqueous medium. The effects of the overall concentrations of the substrate and the surfactant, of the electrolyte concentration, and of the dielectric constant of solubilized water on the enzymatic activity are also investigated. The computations have been carried out for α-chymotrypsin-catalyzed hydrolysis of N-glytaryl- l-phenylalanine- p-nitroanilide in reverse micelles of Aerosol OT in isooctane. The pH near the enzyme surface is found to be more basic than the pH of the stock solution. This causes an acidic shift in the pH-dependent enzymatic activity in the water pool (as compared to that in the bulk aqueous medium). The enhanced activity is due to the enhanced substrate concentration near the enzyme surface which is caused by the pushing of the substrate away from the likewise charge reverse micellar surface toward the enzyme surface, and by the higher average substrate concentration in the much smaller volume of the water pools than that defined on the basis of the entire micellar solution. The increase in the absolute value of the charge of the surface of the RM with increasing W 0 and the increased water pool width act in opposite directions. These effects together with the decrease in the average substrate concentration in the water pool as W 0 increases at constant [ S 0] ov are responsible for the bell-shaped dependence of the substrate concentration at the enzyme surface on W 0 which, in turn, causes the bell-shaped dependence of the activity on W 0. However, enhanced activity is observed only at relatively small overall surfactant concentrations. At relatively high surfactant concentrations, the enzymatic activity is found to be smaller than that in the bulk aqueous medium. This is due to the fact that a greater amount of the substrate partitions into the surfactant layer and, therefore, less substrate is available for reaction in the water pool. The dielectric constant of the water pool has a significant influence on the enzymatic activity in reverse micelles and also on the position of the optimum hydration ratio. The enzymatic activity also depends on the concentration of the electrolyte in the solution, decreasing with increasing electrolyte concentration. The theoretical results obtained here have been found to agree, both qualitatively and quantitatively, with the experimental results available in literature.