SiO2 and MgO in the metallurgical slag of nickel laterite have great recycling values. In this work, SiO2 was first separated from the slag by a procesv of sodium hydroxide melting and water leaching, and then MgO in the residues was extracted in molten NaOH. The effects of temperature, time and the mass ratio of sodium hydroxide to slag on the silica leaching rate were investigated. The results show that the optimal melting experimental conditions of Mg2SiO4 in molten NaOH can be obtained at reaction temperature of 450 ℃, reaction time of 90 min and the mass ratio of sodium hydroxide to slag of 3:1. X-ray diffraction (XRD) analysis indicate that the imitative slag reacts with molten NaOH to generate sodium silicate and Mg(OH)2, where the former can be dissolved in water and the latter is precipitated.