Biodiesel is a renewable fuel, consistituting an alternative to petroleum-based diesel fuel. It is non-toxic and biodegradable and has a low emission profile, is better from environmentally sensitive areas. Research study on alternative fuels is essential for increased energy security. Transesterification of Jatropha curcus oil is carried out in the presence of methanol and potassium hydroxide (KOH) as catalyst, keeping the molar ratio of oil to alcohol 1:6, catalyst concentration 0.75 wt% of oil, ultrasonic amplitude 60% and pulse 0.3 cycles, 7 min reaction time under atmospheric condition. Ultrasonic mixing has increased the rate of transesterification reaction as compare to the mechanical mixing.