The catalytic properties of Y zeolites, dealuminated by steam stabilization, for the transalkylation of toluene with trimethylbenzene were investigated in a pulse microreactor. Some factors influencing this reaction were taken into account : the reaction temperature, the degree of dealumination, the nature of acid sites and the deposited coke. The transalkylation reaction proceeds with good yields on USY. At bulk silica to alumina ratio’s around 5, a higher activity is observed for the transalkylation of toluene than for the disproportionation of trimethylbenzenes. Both HNaY and USY samples were characterized using FTIR and XPS of chemisorbed pyridine. These techniques allowed to detect the presence of the three kinds of acidic sites : the Bronsted acid sites, the Na+ cations and the extra framework AlO+ species. The effect of these three sites on catalytic results are discussed as well as the reactivity of alkylaromatic hydrocarbons in the reaction network and the reaction mechanism.