A chemical kinetic model for i-butane and n-butane catalytic cracking over synthesized HZSM-5 zeolite, with SiO2/Al2O3 = 484, and in a plug flow reactor under various operating conditions, has been developed. To estimate the kinetic parameters of catalytic cracking reactions of i-butane and n-butane, a lump kinetic model consisting of six reaction steps and five lumped components is proposed. This kinetic model is based on mechanistic aspects of catalytic cracking of paraffins into olefins. Furthermore, our model takes into account the effects of both protolytic and bimolecular mechanisms. The LevenbergMarquardt algorithm was used to estimate kinetic parameters. Results from statistical F-tests indicate that the kinetic models and the proposed model predictions are in satisfactory agreement with the experimental data obtained for both paraffin reactants. (C) 2011 American Institute of Chemical Engineers AIChE J, 58: 24562465, 2012