This work reports the production of fatty acid ethyl esters (FAEE) by means of Macauba (Acrocomia aculeata) coconut oil (MCO) solvent-free enzymatic transesterification reactions using a commercial immobilized lipase (Novozym 435) under the influence of ultrasound irradiation. An experimental design was used to evaluate the effects of temperature (40-70 degrees C), enzyme (5-20 wt%) concentration, oil to ethanol molar ratio (1:3-1:10) and output irradiation power (40-70% of the maximum supply value) on the reaction yield. Besides, a kinetic study varying the enzyme concentration was also carried out. Results show that ultrasound-assisted lipase-catalyzed transesterification of MCO with ethanol in solvent-free system might be a potential alternative route to conventional alkali-catalyzed and/or traditional enzymatic methods, as reaction yields around 70 wt% were obtained at mild irradiation power supply (similar to 132 W), and temperature (65 degrees C) in a short reaction time, 30 min. Reutilization of enzyme showed that it may be advantageously employed up to 5 reuse cycles. (C) 2014 Elsevier Ltd. All rights reserved.