A kinetic model of lumps has been established for n-butane cracking over HZSM-5 zeolite catalyst (SiO2/Al2O3 = 30) in the 400-550 degrees C range, based on the results obtained in a fixed bed reactor (space time, up to 2.4 (g of catalyst) h (mol CH2)(-1); He/n-butane molar ratio in the feed, up to 6/1; time on stream, 5 h). The model allows quantifying the distribution of the lumps of products (C-2-C-4 olefins, C-2-C-4 paraffins, methane, and C-5-C-10 components) in a wide range of temperatures, partial pressures of hydrocarbons in the reaction medium, and space times. The kinetic model steps for the transformation of n-butane into olefins and of olefins into paraffins and C-5-C-10 are second order with respect to the reactant, whereas the remaining steps are first order with respect to each reactant. When the target is the production of C-2-C-4 olefins, the yield is limited to 12%, at 550 degrees C.