Candida rugosa lipase has been used to investigate the hydrolysis of palm oil in a lecithin/isooctane reversed micellar system. The reaction obeys Michaelis-Menten kinetics for the initial conditions. Kinetic parameters such as maximum rate and Michaelis constant (K-m) were determined for lipase-catalyzed hydrolysis in n-hexane and isooctane. According to the K-m values, the enzyme affinity towards the substrate was increased in isooctane. The maximum degree of hydrolysis was generally decreased as the initial substrate concentration was increased. This may suggest that the hydrolysis in lecithin reversed micelles should be regarded as a one-substrate first-order reversible reaction. It is shown in this study that the proposed one-substrate first-order kinetic model can serve for the precise prediction of the degree of hydrolysis for a known reaction time or vice versa, when the initial substrate concentration is less than 0.325 mol/dm(3). A disagreement with this model was found when the initial substrate concentration was higher than approximately 0.3 mol/dm(3). This may be due to the effects of the products on lipase activity or even to the conversion of the reversed micellar system to other systems.