We report studies of the enzymatic activity of alpha-chymotrypsin (CHT) in aqueous buffer and AOT reverse micelle with various degrees of hydration using the substrate Ala-Ala-Phe-7-amido-4-methylcoumarin (AMC). From Michaelis-Menten kinetics, we determined equilibrium and rate constants for catalytic activity in aqueous buffer. In the reverse micelle we found that the activity of CHT to be retarded by two orders of magnitude compared to that in aqueous buffer. The activity is also found to be nearly insensitive to the degree of hydration of reverse micelle. From these studies, we attempt to elucidate the influence of hydration oil enzyme activity. (C) 2004 Elsevier B.V. All rights reserved.