The binding position and the electronic properties of acidic proton in anhydrous dodecatungstophosphoric acid, H 3 PW 12 O 40 , were studied by means of 1 H, 2 H NMR, and 1 H-31 P spin-echo double resonance (SEDOR) NMR techniques. 1 H 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 PW 12 O 40 3provides a single site to the acidic proton. 2 H NMR spectrum leads to the quadrupole coupling constant (QCC) of 210 kHz and the asymmetry parameter of the electric-field-gradient tensor (η) 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 1 H-31 P SEDOR signal was observed, due to the dipolar interaction between the central 31 P 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 cornershared, edge-shared, or terminal oxygen atom of WO 6 unit in PW 12 O 40 3-, the edge-shared oxygen atom seems to be the most probable binding position for the acidic proton.