The present work reports the intensification of ultrasonication assisted synthesis of biodiesel from waste cooking oil using a novel recirculating flow reactor (RFR). Initially, batch synthesis was carried out to obtain the optimum operating parameters such as oil to alcohol molar ratio, catalyst concentration, sonication power amplitude, and power density. It was observed that a maximum of 95% yield was obtained within 40 min of ultrasonication at optimum oil to alcohol molar ratio of 1:6, optimum catalyst (NaOH) concentration of 1% by wt. of oil and power amplitude of 40%. Further, the RFR based ultrasonication process was used for biodiesel synthesis at these optimum operational conditions and its performance evaluated in comparison to the batch process for its yield, product quality and energy efficiency. In RFR mode, the operational effects of flow rate and number of recirculation passes on the biodiesel yield were studied. The maximum yield of 92% was achieved at the flow rate of 0.5 L/min and with 20 recirculation passes. The efficiency of both batch and RFR processes were evaluated and recirculating flow reactor was found to be almost 4.8 times more energy efficient than the batch reactor for the synthesis of biodiesel.