Moessbauer and EPR investigations of heteropolyacides of tungsten and molybdenum with iron as heteroatom were carried out with the aim to get more information on the structure of these types of compounds. Of a special interest were the structures of H5[FeO4W12O36] · 6 H2O, FeH2[FeO4W12O36. 17 H2O and H3[Fe(OH)6Mo6O16] · 4 H2O, compounds which are prepared in a solid state for the first time. The general result is: all compounds investigated are associated to the Keggin or Anderson structure. For all heteroatom lattice sites a distortion of the cubic surrounding postulated in the literature was found. The quantity of the heteroatom anion site distortion is strongly influenced by the kind of the cation