Solid acid catalyst 30% WO3/SnO2 was synthesized and studied by IR, X-ray powder diffraction, solid state Sn-117 NMR and adsorbed pyridine thermodesorption. The catalyst consists of SnO2 grains covered with W(VI) octahedra organized as in heteropolyacids. Its acidity is lower than the acidity of heteropolyacids but higher than that of the analogous catalyst WO3/ZrO2. The catalyst exhibits a high activity when used in the liquid phase acid-catalyzed reactions, but a part of it is washed out by polar solvents or substrates.