Abstract: Sodium bis (2 - ethylhexyl polyoxyalkylene) sulfosuccinates (SEPES) were prepared and used to form the reversed micelles in isooctane. Taking the hydrolysis of olive oil as a model reaction, the effects of average polymerization number ( n) of ethylene oxide and water content on the activity and stability of lipase in the reversed micelles were investigated. It was found that the activity, the apparent turnover number, and the deactivation rate coefficient of lipase in the reversed micelles formed by SEPES at n=2.0 in isooctane were respectively 2.2, 2.1 and 0.39 times, more than those in AOT/isooctane reversed micelles, while the apparent Michaelis constants of lipase in the two systems were of little differ-