Microwave assisted transesterification of castor bean oil was carried out in the presence of methanol or ethanol, using a molar ratio alcohol/castor bean oil of 6: 1, and 10% w/w of acidic silica gel or basic alumina (in relation to the oil mass) as catalyst. Under acid catalysis, the reaction occurred with satisfactory yields using H2SO4 immobilized in SiO2, methanol under conventional conditions (60 degrees C for 3 h) as well as using microwave irradiation for 30 min. The best results were obtained under basic conditions (Al2O3/50% KOH) using methanol and conventional (60 degrees C, stirring, I h) or microwave conditions (5 min). In comparison with conventional heating, the catalyzed alcoholysis assisted by microwaves is much faster and leads to higher yields of the desired fatty esters. (c) 2008 Elsevier Ltd. All rights reserved.