The effects of experimental conditions such as horn tip diameter, ultrasonic power, ultrasonic frequency and enzyme concentrations on biodiesel yield were investigated. The results showed that the application of ultrasound decreased the reaction time from 22–24 h to 1.5 h with the use of 3.5 cm ultrasonic horn, an applied power of 40 W, methanol to oil molar ratio of 5:1 and enzyme concentration of 0.23 wt/wt% of oil