Abstract: A series of MgAlO_x mixed oxides were prepared by calcination of hydrotalcite materials at various temperatures ranging from 400 to 700℃. The physical and chemical properties of the catalysts were characterized by XRD, TG, N₂ adsorption/desorption, NH₃-TPD, and CO₂-TPD techniques. The catalytic activity was evaluated by the condensation of formaldehyde and acetaldehyde. The results show that as the calcination temperatures increase, both the conversion of acetaldehyde and the space time yield of propanal first increase and then decrease, which shows the same trend with the amount of moderate basic sites, and the C-550 catalyst has the maximum of 39.22% and 103.86 g/(kg·h), respectively. Moreover, the yields of by-products including methanol and CO₂ are also significantly related to the moderate and strong basic sites.