A microkinetic model for the catalytic cracking of n-heptane is proposed comprising a set of significant elementary steps which generate a complex reaction network. This approach constitutes a compromise between fundamental and Jumped models since the reaction scheme is detailed to the carbon atom level by considering separately olefins, paraffins and adsorbed carbenium ions with the same carbon atom number. Elementary rate constants are estimated through expressions relating species reactivity with their carbon atom number. Fitting the model against experimental data over a large parameter space was performed using a micro-genetic algorithm with binary encoding and logarithmic distribution. The advantage of this approach is that it allows modelling the reaction network without supposition of rate determining steps. The model predicts very well the observed transient activity for n-heptane cracking over H-USY zeolite at 623 K and in general, it reasonably predicts the experimental trends for the products distribution. (C) 2003 Elsevier Ltd. All rights reserved.