The activity of different zeolite catalysts in the cotransformation of pseudocumene mixtures with naphthalene and methylnaphthalenes in the autodynamic regime, i.e., under a vapor pressure of components at the reaction temperature (350 degrees C), was compared. The conversion of the methylated aromatic compounds increases with an increase in the degree of ion exchange in zeolites Y and decreases with an increase in the SiO2/Al2O3 ratio in high-silica zeolites. The prevalent reactions are isomerization, disproportionation, and transmethylation, although they are accompanied by the formation of high-molecular-mass naphthyl-containing compounds, which deactivate the catalyst. At a mole ratio of the methyl groups to the aromatic rings of 2.4 (60 mol % pseudocumene + 40 mol % methylnaphthalenes mixture), the proportion of dimethylnaphthalene in the products reaches 13 mol %. It was found that the presence of methylnaphthalenes in the reactant mixture noticeably suppresses the transformation of pseudocumene. The experimental data were compared with equilibrium concentrations calculated for mixtures of methylbenzenes and methylnaphthalenes.