Calcined Mg-Al hydrotalcites (CHT) with various Mg/Al atomic ratios were prepared and characterized by XRD, BET and TPD of carbon dioxide. The CHT catalysts were utilized for the synthesis of alpha -pentylcinnamaldehyde (alpha -P-c) from benzaldchyde and n-hcptaldehyde in a stirred batch autoclave reactor. An increase of Mg/Al atomic ratio of CHT samples results in the apparent enhancement of catalyst basicity with concomitant decrease of surface areas. Both the catalytic activity and the alpha -P-c selectivity increase with the catalyst basicity and the reaction temperature.