A research using ferronickel slag, the by-product of ferronickel production, as raw material for magnesium extraction has been carried out. It is essential to upgrade the value of ferronickel slag instead of used directly for reclamation materials. Moreover, accumulation due to increasing ferronickel demand as well as environmental contamination due to various potencially toxic elements contained in the ferronickel slag could be prevented. The general objective of this study is to utilize the ferronickel slag for magnesium materials. The specific objective is to determine the optimum conditions of magnesium extraction in the process of alkali fusion followed by hydrochloric acid leaching. A novel method for magnesium extraction from ferronickel slag was carried out through reducing silica content followed by acid leaching method. Alkali fusion of the mixture of ferronickel slag and Na2CO3 at 1000 ?C for 60 minutes followed by water leaching at 100 ?C for 60 minutes with solid to liquid percentage of 20 % were carried out to separate the silica. The leaching residue resulted from water leaching was then leached using hydrochloric aid solution to extract magnesium. The leaching temperature and time as well as the hycrochloric acid concentration were varied in the acid leaching process. Alkali fusion process proved can be generated the sodium silicate that can be separated in the water leaching to the leached solution. Meanwhile, the leaching residue was leached using hydrochloric acid to extract the magnesium. The highest magnesium extraction percentage is 82.67% that resulted from an optimum acid leaching condition with temperature of 80 ?C for 30 minutes using 2M HCl solution. Based on the kinetics study, the activation energy (Ea) for the leaching reaction of magnesium at atmospheric pressure between 32?C to 80?C is 9.44 kJ/mol and affected by diffusion and chemical reactions.