The aromatization of a-pinene in the vapor phase over chromia gel and chromia-alumina catalysts prepared from aluminas of different acidity has been studied. The acidity of alumina support has a remarkable influence on the composition of the aromatics resulting from the dehydrogenation of a-pinene. Over weakly acidic chromia-alumina doped with 1% sodium catalyst, a-pinene is aromatized to p-cymene, 1,2,4-and 1,2,3-trimethylbenzenes with traces of toluene and xylenes, whereas over the strongly acidic chromia -pure alumina and chromia-alumina containing 5% H F catalysts it gives considerable amount of m-cymene, toluene, and tetramethylbenzenes. A satisfactory mechanism to explain the formation of these compounds is offered.