Magnesium was enriched in residue obtained by alkali baking the laterite nickel ore baked,following digestion in water of clinker and filtration of slurry.Employing the residue as raw material,industrial (NH4)2SO4 as leaching reagent, magnesium was leached out from the residue by counter-current leaching method.Partial nickel was also leached out from the residue.Based on the single factor experiments, the orthogonal experiments were adopted to optimize the reaction conditions and the appropriate reaction conditions were obtained.The main components of the leaching residue were examined to check the extraction rate of Mg.The leaching solution after nickel precipitation was used to prepare the Mg product with ammonium carbonate.The MgCO3·SH2O was successfully obtained and the influences of the reaction temperature, reaction time and ratio of materials on the precipitation rate of Mg were discussed.MgO was yielded out after the MgCO3· 5H2O roasted at 700C.Both MgCO3·5H2O and MgO were characterized by XRD and SEM, and the MgO powder was in line with the industry standard.