Comparative studies of lipase-catalyzed hydrolysis of soy oil in solvent-free system were carried out in shaking bath and in ultrasonic bath. A suitable ultrasonic power of 1.64 W cm(-2) was determined to guarantee satisfactory hydrolysis extent and lipase activity. The influence of temperature, pH, enzyme concentration and water/oil ratio was investigated subsequently. Compared with that in shaking bath, optimum temperature and inactivation temperature of lipase in ultrasonic bath were about 5-10 degrees C higher, while pH effect in ultrasonic bath was similar; ultrasound also led to a smooth increase of reaction rate at relatively higher enzyme loading and less use of water to saturate hydrolysis substrate. In optimum conditions, the overall hydrolysis reaction rate in the ultrasonic bath process was above 2-fold than that in the shaking bath process.