Sulphonated resins used in the industry as the catalysts in the synthesis of methyl tert-butyl ether (MTBE) until now, the most important anti-knocking additive to the gasoline, are not satisfactory because of environmental reasons and catalyst's not adequate stability. This stimulates the search for new catalysts for this process. Among others heteropoly acids (HPA) are considered to be prospective ones. The present paper is the review of the authors' investigations on physical chemistry of the MTBE synthesis in gas phase on dodecatungstosilicic acid H4SiW12O40 (HSiW). It has been preceded by the study of the interaction of both substrates, methanol and iso-butylene and the product MTBE, with crystalline HSiW comprising classical sorption experiments, FTIR and calorimetric measurements. Together with reaction kinetic measurements it enabled to propose the mechanism of the catalytic reaction according to which iso-butylene not penetrating the bulk of HSiW crystallites gets protonated at the surface with the loosely bonded protons (protons forming hydrogen bond between HSiW anions) and subsequently reacts with methanol from next-to-surface layer or from the gas phase. Methanol penetrating into the bulk is forming protonated clusters thus diminishing the concentration of loosely bonded protons. At high enough methanol concentration this leads to the diminishing of the formation rate of carbocation. In the result reaction order positive at the initial state of catalytic process (low bulk concentration of methanol and high concentration of loose protons) turns into negative at the reaction steady state. A set of kinetic equations has been proposed describing all these processes. A series of oxide supports: SiO2, TiO2, SiO2-Al2O3, gamma-Al2O3 and AlPO4 with increasing basicity (characterised by the net oxygen negative charge calculated according to Sanderson's theorem) was used for the preparation of HSiW supported catalysts. It has been shown that the activity decreases with the increasing basicity as a result of strong bonding protons by the surface of the support. (C) 2003 Elsevier B.V. All rights reserved.