The Ni/CaO catalyst for the synthesis of 3,3,5-trimethyl-2-cyclohexene (isophorone)from acetone was studied. CaO and CaO incorporated with Co, Fe, and Cu did not show the activity. However, when 4 wt% Ni was incorporated into CaO, isophorone was much detected suggesting that Ni played an important role in catalytic activity. The 4 wt% Ni/CaO reduced at 700℃ showed 8~50% of acetone overall conversion and 69~85% of isophorone selectivity. With the increase of Ni loading to 20 wt%, the acetone overall conversion and the selectivity for isophorone were decreased to 6~24% and 40~73%, respectively.