Hydroxide-catalyzed methanolysis kinetic reaction model that considers the side effects of saponification of glycerides, esters and free fatty acids (FFAs) was proposed. Methanolysis of a mixture of Jatropha curcas-waste food oil that contains 1%wt FFAs under reaction temperature 50 degrees C, mixing speed 900 rpm, methanol to oil molar ratio 6:1 and KOH to oil mass ratio 1%wt, was accurately and completely described by the kinetic reaction model. Simulation and experiment results showed that the FFAs were neutralized by the hydroxide ion, resulting in production of water and more soap. This was undesired side reaction because it consumed more catalyst to achieve the same reaction rate. However, 1%wt FFAs content in the oil mixture and 2 h reaction time of methanolysis produced biodiesel with 97.1%wt purity. (C) 2010 Elsevier Ltd. All rights reserved.