The isopropanol decomposition reaction was used to evaluate the catalytic activity of ultrastable (USY) zeolites with different degrees of dealumination, treated in strongly alkaline medium at various temperatures and contact times. This treatment resulted in the reinsertion of non-framework aluminium, a result of the ultrastabilization process. The samples obtained were also submitted to an acid treatment, leaching the non-framework aluminium that had not been reinserted. The results obtained at 723K showed a large reduction in the acidic activity of the alkaline-treated zeolite, as the treatment conditions became more severe (the longer the treatment time or the higher the temperature, the higher the degree of dealumination). On the other hand, treated samples displayed some isopropanol dehydrogenation activity (basic sites). However, this activity was not very significant and did not depend on the alkaline treatment or ultrastabilization conditions used. The effect of reaction temperature and acid leaching on activity is also shown.