This study was conducted to compare the effects of ultrasonic energy and mechanical stirring methods in bio-diesel production from rapeseed oil under base catalysis conditions. With the transesterification of rapeseed oil, the molar ratio of methanol to vegetable oil was 6 : 1, and the amount of catalysts added to the vegetable oil was 0.3, 0.5 and 1.0% (wt/wt). The main components of methyl esters from the transesterification of rapeseed oil were oleic acid (48.5%, C18:1) and linoleic acid (18.1%, C18:2). In addition, the optimum conditions to produce fatty acid methyl esters (96.6%) were 0.5% KOH after 25 min of ultrasonification at 40 ℃ as compared to mechanical stirring at 60 ℃. The maximum conversion ratio was 75.6% with 1.0% NaOH after 40 min of ultrasonification at 40 ℃. These results indicate that ultrasonic energy could be a valuable tool for transesterification of fatty acids from rapeseed oil in terms of the reaction time and temperature.