Abstract: A continuous process for producing biodiesel fuel with a conversion of triglycerides in biodiesel above 99.90% by weight in the transesterification step, which comprises the following steps: a) providing a triglyceride source at a triglyceride concentration above 99.0% by weight; b) subjecting triglycerides to a transesterification reaction with methanol, ethanol, or the mixtures thereof, at a molar ratio of triglycerides:alcohol 1:3-3.5, in the presence of 0.7 to 1.0% by weight of sodium or potassium hydroxide as catalyst, under ultrasonic cavitation conditions in an ultrasonic cavitation reactor with 2 to 8 serial cavitation cells, at a temperature of 45 to 60° C., at a pressure of 1.5 to 2 MPa (15-20 atm) and during a period of time of 15 to 30 seconds; c) recovering the product of step b) and subjecting it to mechanical agitation operation, at a temperature of 45 to 60° C.