One step synthesis of MIBK from acetone over Ni/CaO catalysts was studied. 10 wt% Ni/CaO catalysts were prepared by conventional impregnation method (catalyst I), and liquid phase oxidation method using NaOCl as an oxidant (catalyst L). Catalyst L showed much higher activity than catalyst I because of recovered CaO pore structure and high BET surface area. Catalyst C, prepared by coprecipitation method, showed 60% of MIBK selectivity with a fairly high overall acetone conversion. Catalysts L and C had two CO₂ desorption states(α, β). Incorporated Ni enabled support precursor [Ca(CO)₃] to decompose easily into CaO and CO₂ even at low temperature and generated weak CO₂ desorption state(α) which was from active state.