A polyaniline-supported dodecatungstosilicic acid H4SiW12O40 catalyst was tested in the electrophilic addition of methanol to isobutene resulting in methyl-tert-butyl ether. The activity of the catalyst is poor after pretreatment in helium gas, but increases one order of magnitude after activation in air at 473 K. FTIR and XPS investigations indicated that the latter treatment is accompanied by the migration of protons from the bulk of the polymer matrix to the surface, thus increasing the concentration of the Bronsted acid centers considered to be catalytically active sites.