The effects of the introduced Lewis acid sites of different kind (InO+ or AlO+) and the variation of InO+ concentration on the catalytic behavior of dealuminated in solid-state HY zeolites in the reaction of cumene-toluene transalkylation have been studied. The catalysts, indium modified HY(3.7) and ultra stable zeolite USY(3.4), containing essentially equivalent amounts of framework aluminum and Lewis acid sites (InO+ and AlO+, respectively), have been compared to the initial HY(3.7), not containing any extra-framework aluminum (EFAI). Strictly controlled conditions were used for the formation of Lewis acid sites: through reductive solid-state ion exchange (RSSIE) for InO+ or by steaming in the case of AlO+. The ratio between the Lewis and Broensted acid sites was varied by progressive replacement of the protons by InO+ cations in HY(5.6) zeolite. The zeolites modified by monovalent (InO+ and AlO+) have, as a result, an enhanced catalytic activity in comparison with HY(3.7). This effect is mainly due to intense side reactions of dealkylation, oligomerization, cracking and re-alkylation at the expense of the cymenes formation. The data for the distribution of the reaction products suggest a highly preferred mechanism of dealkylation/alkylation with the increase of the Lewis/Broensted acid site ratio. The presence of cation-connected Lewis acid sites is supposed to be responsible for the fast samples' deactivation. (C) 2003 Elsevier Science B.V. All rights reserved.