The effects ofmolar ratio of methanol to oil, ultrasonic power, catalyst dosage and reaction temperature on the yield of fatty acid methyl ester in transesterification reaction of lardare studied by single factor method with lard and methanol as raw material, KOH as catalyst. The results show that the optimum value for all the factors are methanol/oil molar ratio 6∶1, ultrasonic power 120 W, catalyst dosage 0.8% (based on oil) and reaction temperature 60 ℃. Response surface methodology is applied to optimize homogeneous KOH-catalyzed transesterification. The results show that the optimal condition are methanol to oil ratio of 5.8∶1, ultrasonic power of 135.91 W, reaction temperature of 52.78 ℃, catalyst dosage of 0.86%, in which theoretical conversion achieve 99.53%.