An application of Ni/MgO catalyst which was prepared by using citric acid to the hydrogenation of carbon dioxide was investigated. The Ni/MgO catalysts with Ni content higher than 30 wt% were found to exhibit high catalytic activities for the hydrogenation of carbon dioxide due to the large Ni metal surface area. The usage of citric acid realizes the formation of NiO-MgO solid solution at a low temperature of 773 K. Aggregation of Ni metal particle is probably depressed by MgO highly dispersed in the Ni particle during the reduction of the NiO-MgO solid solution. A structural model of the Ni catalyst is proposed.