The strength and distribution of Brønsted acidic protons in anhydrous phosphomolybdic acid (H 3 PMo 12 O 40 , HPMo) have been studied by solid-state magic-angle-spinning (MAS) NMR, using trimethylphosphine oxide (TMPO) as the probe molecule in conjunction with density functional theory (DFT) calculations. Brønsted acid sties with strengths exceeding the threshold of superacidity (Zheng, A. et al. J. Phys. Chem. B 2008, 112, 4496) were observed for HPMo. In addition, the locations and adsorption structures of Brønsted protons on various oxygen sites in HPMo were also identified. The preferred location of the acidic proton was found to follow the trend: corner-sharing (O b ) > edge-sharing (O c ) . terminal (O d ) sites. Moreover, a tendency of hybridization among Brønsted protons residing at O b and O c sites of HPMo was inferred by experimental as well as theoretical 31 P chemical shifts of the adsorbed TMPO.