The present work illustrates the incorporation of ultrasound and its improved impact in the lipase catalysed esterification. Synthesis of isoamyl butyrate from isoamyl alcohol and butyric acid using immobilised Novozym 435, has been carried out in the presence of ultrasound. The optimisation of various parameters affecting the synthesis of ester in presence of ultrasound was done. The systematic experimentation involves change of one working parameter at one time while keeping the others constant. For the maximum conversion, optimum parameters such as the ultrasound of 25 kHz frequency with power of 70W, at the temperature of 60 degrees C with stirring speed of 80 rpm, mole ratio of alcohol:acid followed as 2:1, use of molecular sieves weighing 2g. with immobilised enzyme loading of 2% (m/v) and duty cycle of 83%, were obtained. The optimum parameters collectively, gave 96% conversion of the product in 3 h as compared with 10 h in absence of ultrasound. The immobilised biocatalyst, Novozym 435 has an added benefit of reusability till 7 repetitive cycles. Besides, the synthesis is executed in the solvent free system that contributes the production of flavour in greener way. (C) 2014 Elsevier Ltd. All rights reserved.