This work reports the enzymatic hydrolysis of soybean and waste cooking oils in ultrasound system towards producing free fatty acids hence allowing faster esters production. For this purpose, the following experimental conditions were investigated: temperature (40–60°C), molar ratio of oil to water (1:9; 1:10; 1:20, 1:40 and 1:46), enzyme (Lipozyme TL IM) concentration (1–10wt%, based on the total mass of substrates), keeping the reaction time fixed at 2h, 300rpm stirring rate and ultrasonic output power of 132W. Results showed a content of 60wt% FFA for soybean oil while 61wt% was reached for waste cooking oil. After the experimental design, a kinetic study was performed at the best temperature, molar ratio (oil:water), enzyme concentration varying reaction times (until 24h) with and without ultrasound. The use of ultrasound showed to be effective, increasing the initial reaction, providing very satisfactory reaction yields at short reaction times with no damage to protein structure thus allowing enzyme reuse.