O-17 MAS NMR spectra for solid heteropoly acid (HPA) H3PW12O40 are reported. Comparison of solid-state and solution O-17 resonances shows that in the solid dehydrated H3PW12O40 terminal W=O oxygen atoms are the predominant protonation sites. H3PW12O40 and H4SiW12O40 supported on chemically activated carbon have been studied by means of NMR, FT-IR and XRD. The carbon-supported HPA’s retain their Keggin structure and form finely dispersed HPA species. No HPA crystal phase is developed even at an HPA loading as high as 45 wt%. P-31, Si-29 and O-17 MAS NMR spectra for bulk and carbon-supported HPA’s indicate interaction of the HPA Keggin units with the carbon surface, causing large line broadening in the NMR spectra.