Biodiesel is one of the alternative fuels that can help in reducing oil dependence. beta-Zeolite was modified with phosphoric acid and the modified beta-zeolite was used as catalyst for the esterification of free fatty acids (FFA) present in pinnai oil and its effect on esterification reaction was studied. Influence of catalyst amount, methanol to oil ratio and temperature on specific reaction rate was modelled using LangmuirHinshelwood (LH) kinetics, pseudo first order kinetics and Arrhenius equation, respectively. The kinetic constant values obtained in LH kinetics show that the adsorption capacity of FFA on catalyst surface was approximately 23 times higher than that of methanol. From pseudo first order kinetic modelling it is found that methanol to oil molar ratio of 9 gives the optimum k value. Thermodynamic studies were also performed to prove the endothermic nature of P beta catalysed esterification reaction. (c) 2011 Canadian Society for Chemical Engineering