Background: The synthesis of butyl butyrate (used as a pineapple flavor) by green chemistry is of immense importance to the food industry. This study investigated the enzymatic esterification of butanol and butyric acid to butyl butyrate and transesterification of ethyl butyrate to butyl butyrate in supercritical carbon dioxide (ScCO2) with a lipase, Novozym 435. Results: The effect of various parameters, such as temperature and enzyme, loading was investigated. The initial rate increased sharply up to 3% (w/w) and 7% (w/w) of enzyme loading for esterification and transesterification, respectively while further addition of enzyme did not increase the initial rate significantly. The optimum temperature for the reaction was between 45-50 °C. Because lipases can catalyze both esterification and hydrolysis, a complete kinetic model accounting for both reactions was developed and used to determine the kinetic parameters. Conclusions: Butyl butyrate was successfully synthesized in supercritical carbon dioxide in the presence of a lipase. The kinetic parameters for esterification, hydrolysis and transesterification were determined using the Ping-Pong Bi-Bi mechanism with substrate inhibition and represented by the Lineweaver and Burk plot. © 2008 Society of Chemical Industry.