Mg-Al hydrotalcite-derived oxides with a varying Mg/Al molar ratio, ranging from 2.6 to 3.2, were rehydrated in the vapor phase at different temperatures (20-90 degrees C). The catalytic performance of the materials obtained was studied in the aldol condensation of acetone. The initial activity of the rehydrated catalysts depended strongly on the Mg/Al molar ratio and the activation temperature. It was found that the re-arrangement of active sites, leading to the reconstruction of hydrotalcite-like phase, occurred during the catalytic test.