The binding position and the electronic properties of acidic proton in anhydrous dodecatungstophosphoric acid, H3PW12O40, were studied by means of H-1, H-2 NMR, and H-1-P-31 spin-echo double resonance (SEDOR) NMR techniques. H-1 broad line NMR spectrum showed a bell type resonance line shape with 4.7 kHz line width and MAS NMR spectrum has a single resonance peak, suggesting that the hetero-polyanion PW12O403- provides a single site to the acidic proton. 2H NMR spectrum leads to the quadrupole coupling constant (QCC) of 210 kHz and the asymmetry parameter of the electric-field-gradient tenser (eta) Of 0.15. The value of QCC suggests that the deuterons are bonded to oxygen atoms in the hetero-polyanion very rigidly, and that any motion of the hetero-polyanion does not take place. A remarkable decay of the H-1-P-31 SEDOR signal was observed, due to the dipolar interaction between the central P-31 and three protons strongly bonded to the hetero-polyanion. The P-H distance was evaluated by simulating the decay behavior of the echo to be 0.50 +/- 0.02 nm. Comparing this P-H distance with model structures in which protons are bonded to corner-shared, edge-shared, or terminal oxygen atom of WO6 unit in PW12O403-, the edge-shared oxygen atom seems to be the most probable binding position for the acidic proton.