A series of hybrid heteropoly acid (HPA)/zeolite catalysts has been prepared by supporting 12-tungstophosphoric acid (H3PW12O40) on a faujasitic matrix. It has been shown that the structure of a dealuminated zeolite Y is retained upon contact with a very strong solid acid. The catalytic properties of the hybrid catalysts were examined in the two gas-phase reactions: disproportionation of toluene and transalkylation of toluene and 1,2,4-trimethylbenzene (1,2,4-TMB). All the hybrid catalysts exhibit enhanced catalytic activity in both processes. Already the small amounts of heteropoly acid exert significant influence on the activity in both reactions studied. A pronounced shape-selectivity, expressed as p-xylene/o-xylene ratio, is evident both in toluene disproportionation and its transalkylation with 1,2,4-TMB at low temperatures, while equilibrium distribution of xylene isomers is typical at higher temperatures. As evidenced by P-31 NMR, two types of the Keggin unit are present in the catalysts. They are located in the mesopores of zeolite and on the zeolite crystals, respectively. The Keggin units interacting strongly with the support, characterised by chemical shift at - 13.3 ppm and located in mesopores are probably the more active ones in title reactions. (C) 2003 Elsevier B.V. All rights reserved.