The industrial processes of biodiesel production most commonly employed are based on the transesterification of vegetable oils with methanol and homogeneous catalysts in mechanically stirred batch reactors. Among recent advances in transesterification processes, employment of ultrasound stands out for its effective improvements to the process, both in terms of degrees of conversions and of reducing reaction times and energy consumption. Moreover, the production units tend to be more compact. The present work aimed at the development and testing of a biodiesel production unit with ultrasound-irradiated circulation flow reactor for vegetable oils transesterification. A comparison between conventional process (mechanical stirrer) and indirect irradiation (flow cell) was performed to verify the effectiveness of the circulation flow reactor. The effects of various parameters, such as oil/methanol molar ratio, catalyst loading, residence time, and temperature, on reaction yield were studied to optimize the process. The developed reactor allowed for increases in ester yield, decreases in reaction times, reduction in reagent consumption and consequent energy savings in regard to the conditions for a conventional batch stirred reactor. (C) 2015 Elsevier Ltd. All rights reserved.