The Claisen-Schmidt condensation between benzaldehyde and acetophenone has been carried out in the presence of calcined-rehydrated hydrotalcites as solid-base catalysts. The rehydration method and the effect of the water content as well as the chemical composition of the rehydrated Al-Mg mixed oxides have been studied. The results showed that an Al-Mg mixed oxide with an Al/(Al + Mg) molar ratio of 0.25 with a water content of 35 wt% was the optimum catalyst which gives excellent activity for this type of condensation. This optimized catalyst has been applied to the synthesis of several chalcones with antiinflammatory, antineoplasic, and diuretic pharmacological activities achieving in all cases excellent activity and selectivity to the corresponding chalcones. A comparative study in the homogeneous phase using KOH as base catalyst showed that the rehydrated Al-Mg mixed oxides can compete with the conventional KOH when the reaction is performed at higher reaction temperatures. This behavior is not attributed to a lower intrinsic activity of the active sites on the solid, but to the small concentration of accessible active sites existing on the rehydrated sample. (C) 2003 Elsevier Inc. All rights reserved.