Kinetic determinations of the cracking and catalytic decay of n-heptane, n-decane, n-dodecane and n-tetradecane have been carried out on USY, Beta and ZSM-5 zeolites by means of an experimental set which allows to take samples of products coming out from the reactor at very short time on stream. The influence of the zeolite properties on the catalytic activity and catalyst decay has been obtained. By studying the evolution of the rate constants with the number of carbon atoms in the n-alkanes it has been found that the existence of a PCP cracking mechanism would be consistent with the observed evolution.