The effect of lithium addition to gamma-Al2O3 on the acidity and on the catalytic behaviour in the isopropanol dehydration reaction is studied. Results show that there is an important blocking or poisoning effect of lithium on the Lewis Al3+ sites of the alumina surface; these sites play an important role in the isopropanol dehydration reaction to di-isopropylether and propylene. The diisopropylether formation is drastically reduced by lithium addition, while the propylene formation can be maintained, even at a high lithium content, by increasing the reaction temperature. Results are interpreted by considering that the ether would be produced by a concerted mechanism (E(2)), and the olefin formation could be carried out by both E(2) or E(1) mechanisms.