The Xe-129 NMR method has been applied to the ammonium and cesium salts of 12-tungstophosphoric, 12-molybdophosphoric, and 12-tungstosilicic acids, as well as to the potassium salt of the first acid. The data obtained provide evidence for the presence of a homogeneous and organized pore structure. The ammonium salts produce similar pore openings of 9.0 Angstrom, regardless of the composition of the anion, while those for the cesium salts are found to be dependent on the nature of the anion.