The ultrasound-assisted sunflower oil methanolysis using KOH as a catalyst was studied at different reaction conditions. A full factorial experiment 3(3) with replication was performed. The effects of three reaction variables, methanol-to-oil molar ratio, catalyst loading and the reaction temperature on fatty acid methyl ester yield were evaluated by the analysis of variance and the multiple regression. At the 95% confidence level all three factors and the interaction of the reaction temperature and methanol-to-oil molar ratio were effective on fatty acid methyl ester formation, the most important factor being the catalyst loading. The relationship between the factors and their interactions was modeled by the second-order polynomial equation. (c) 2010 Elsevier B.V. All rights reserved.