The kinetics of the esterification of free fatty acids (FFA) in sunflower oil with methanol in the presence of sulphuric acid at concentrations of 5 and 10 wt% relative to free acids as catalyst and methanol/oleic acid mole ratios from 10:1 to 80:1 was studied.The experimental results were found to fit a first-order kinetic law for the forward reaction and a second-order one for the reverse reaction.