The kinetics of vapor-phase isomerization of xylenes has been carried out over a USY zeolite catalyst using a fluidized-bed reactor. A comprehensive kinetic model based on the triangular reaction scheme is proposed for the reaction. The rate constants and activation energies are estimated from simplified, effective kinetic models based on the isomerization of the pure xylene isomers. The obtained results confirm an earlier proposition in the literature that the mutual interconversion of p- and o-xylenes in 1,3-methyl shifts is quite difficult as compared to intramolecular 1,2-methyl shifts. The riser simulator and associated modeling techniques are shown to be effective tools in investigating the kinetics of xylene isomerization.