beta-Keto esters serve as important synthons since they can be easily transformed into chiral building blocks via enzymatic transformation. As a consequence, their inter-conversion into different esters has gained a great deal of attention. This work focuses on the transesterification of methyl acetoacetate, a beta-keto ester, with various alcohols in the presence of immobilized lipases the influence of microwave irradiation. A number of commercially available lipases such as Novozym 435, Lipozyme RM IM and Lipozyme TL IM were screened and Novozym, 435 was found to be the most active. The effect of chain length of alcohol was also studied. There is a synergism between the enzyme catalysis and microwaves. The reaction follows the ping pong bi-bi mechanism. The theoretical predictions and experimental data match very well. (C) 2004 Elsevier B.V. All rights reserved.