The isomerization reaction in liquid phase of a -pinene in camphene catalyzed by tungstophosphoric acid supported on silica is studied. The catalyst is characterized with FT-IR and XRD to establish if the tungstophosphoric acid maintains the Keggin structure after being supported. The catalyst acidity exposed to different thermal treatments was determined by using FT-IR and TPD techniques of ammonia adsorbed. Two types of sites are distinguished, weak acid sites and strong acid sites. The weak acid sites concentration increases with the thermal treatment and can be responsible for the selectivity decrease in camphene by formation of products of higher molecular weight, while the strong acid sites concentration remains almost constant affecting in a lesser degree the obtention of monocyclic compounds