Methanesulfonic acid has been used as a catalyst for the esterification of free fatty acids (FFA) present in jatropha oil with methanol. The reaction kinetics are estimated for 1 to 2.5 wt% catalyst concentrations, temperature from 45-60 degrees C and methanol-FFA mole ratios ranging from 10:1 to 25:1. The optimum conditions are found to be 20:1 methanol-FFA mole ratio and 1 wt% catalyst at 60 degrees C and 400 rpm for 270 min which give a maximum conversion of 97.9%. A second-order kinetic model for both the forward and backward reactions is proposed to study the reaction. The effect of temperature on the reaction rate constants and equilibrium constant has been determined using Arrhenius and von't Hoff equations respectively. The heat of reaction is found to be 25.936 kcal/mol.