The vapor-phase aldol condensation of formaldehyde with acetaldehyde was studied using various oxide mixtures obtained in situ from hydrotalcite-like materials as catalysts. All samples exhibited catalytic activity, but the selectivity to both the aldol condensation and the acrolein formation is governed by the balance of acidic and basic properties. The oxides containing Mg and Al or Co and Al showed a high selectivity to aldol condensation (90% at 300 degrees C) as well as to cross-condensation (80% at 300 degrees C). The effects of both the reaction variables (temperature, mole ratio of reagents) and the catalyst variables (nature of cations, nature of anions) were studied.