The activity of Chromobacterium viscosum lipase (glycerol-ester hydrolase, EC 3.1.1.3) entrapped in AOT/isooctane reverse micelles was significantly increased by the addition of short chain polyethylene glycols (PEGs) or methoxypolyethylene glycols (MPEGs) for the hydrolysis of olive oil. To understand enzyme activity in the presence of PEG 400 or MPEG 550 molecules, a kinetic model was proposed. The validity of this model was verified by experimental data on the lipase-catalyzed hydrolysis of olive oil in AOT/isooctane reverse micellar systems, in which PEG 400 or MPEG 550 had been added. The large value of the equilibrium constant (k(D)) for enzyme activation indicated that the affinity between C viscosum lipase and PEG 400 or MPEG 550 molecules was very strong. The Michaelis constant (K-m) predicted by the proposed model explained enzymatic reactions more exactly than that by the previously published model. (C) 2003 Society of Chemical Industry.