The extended Huckel molecular orbital (EHMO) calculations have been carried out using cluster approach to polyoxo anions, i.e. calculations have been done for a single octahedron MO 6 of different symmetry and results have been used to analyze 1 8 3 W and 1 7 O NMR spectra. Using five d->d* energy differences for the individual WO 6 the sum Σ1/ (E d ->E d *) have been calculated and plotted against the 1 8 3 W chemical shift (from +258 to -670 ppm) for corresponding type of tungsten atom and practically a linear correlation between two parameters have been observed. This points out the electronic nature of the 1 8 3 W chemical shift. Similar correlation have been found for the 1 7 O NMR chemical shifts (-90 to +800 ppm) when the plotted against product of the R - 3 Σ1/ (E p ->E p *) where the R - 3 bond length of the corresponding W-O bond. Increasing the 1 8 3 W nuclear magnetic shielding with the calculated electron population on tungsten atom for closely related anions has been observed, but no general tendency between δ and the calculated electronic charge if the symmetry of polyhedron is changed is expected.