The Wells-Dawson acid was studied as a catalyst for producing methyl tert-butyl ether (MTBE) from methanol and isobutylene in the gas phase at 373 K. Thus, pure Wells-Dawson acid was synthesized and characterized by P-31 NMR, XRD, FTIR and TGA-DTA measurements. The results indicated that the Dawson acid keeps its heteropolyoxoanion structure up to 873 K. The samples were active and very selective (close to 100%) for MTBE production and showed stable behavior during the reaction period of 3 h. The conversion observed on reference catalyst Amberlyst 15-wet under the same conditions was significantly lower. The acid was also tested in methanol dehydration to dimethyl ether at 373 K. For both reactions, the catalytic activity depends on the pretreatment temperature of the acid. The activity was approximately constant up to 473 K; then activity decreased steadily until becoming null when pretreatment temperature was 673 K. The catalytic results were explained using the pseudoliquid phase behavior concept.