This paper reports a kinetic model for the selfepoxidation of oleic acid with toluene as solvent and Novozym 435 (a commercially available preparation of immobilized Candida antarctica lipase) as catalyst at 30°C. The effects of various parameters on the conversion and rates of reaction were studied. Both the initial rate and the progress curve data were used to fit an ordered bi-bi model. At low temperatures, the rate of epoxidation was faster than the rate of deactivation of the enzyme by hydrogen peroxide.Paper no. J9531 in JAOCS 78, 347-351 (April 2001).Epoxidation of olefinic compounds leads to the formation of commercially important precursors that are employed to manufacture glycols, alcohols, carbonyls, alkanolamines, substituted olefins, polyesters, polyurethanes, and epoxy resins. The unsaturation present in fatty acid molecules and their corresponding esters can be harnessed to prepare a gamut of epoxidized compounds. For instance, epoxides of soybean and other vegetable oils have been employed as plasticizers and stabilizers for the plastics of polyvinyl chloride (PVC) and other related resins to improve the flexibility, elasticity, and toughness of the plastics and also to impart thermal and photo stability. Among the various chemical routes available for the synthesis of epoxidized oils, the most important and widely applied one involves the use of a suitable organic peracid (1-4) with an unsaturated oil. The next important process is the oxidation of unsaturated compounds in the presence of aldehydes (5). However, the disadvantage of the latter process is that the aldehyde should be taken in stoichiometric quantities with the acid, leading to by-product formation. As compared to chemical processes, enzyme-catalyzed epoxidations are advantageous from several viewpoints, such as mild reaction conditions and high selectivity/specificity with little or no by-product formation. Self-epoxidation of unsaturated acids with hydrogen peroxide in the presence of a lipase is a novel application of enzyme catalysis (6) because by-products, such as dihydroxy acids and estolides, that are so common in the epoxidation of fatty acids by chemical routes are not formed in lipase-catalyzed epoxidations; the only by-product is a small amount of epoxy-peroxy acid. The formation of carboxylic