Abstract: A series of Mg-Al composite oxide catalysts with different Mg-Al ratios were prepared by co-precipitation method. XRD，BET，and Py-IR methods were used to analyze the prepared catalysts.In a continuous flow fixed bed micro reactor under atmospheric pressure，the performance of Mg-Al composite oxide catalysts was investigated for acetone gas phase condensation reaction to produce isophorone.Results showed that the prepared Mg-Al composite oxides catalysts had higher surface area，and larger average pore and volume；the MA35 catalyst showed the best performance.Under the conditions of reaction temperature of 250 ℃，space velocity of 1 h-1，and 0.1 MPa pressure，the once-through conversion rate of acetone was up to 18.8%，and isophorone selectivity was 46.5% in the acetone gas phase condensation reaction.

Key words: Mg-Al composite oxide, co-precipitation method, acetone, isophorone