In this study, an in-situ formed Mg2Si-Mg composite is investigated to understand the formation of Mg2Si and its influence in mechanical properties and corrosion behavior. A starting blend of 2.5 wt.% SiO2 nanoparticles and magnesium powders was used to elaborate in-situ composite through mechanical blending followed by spark plasma sintering technique. High temperature X-ray diffraction measurements and differential scanning calorimetry results confirmed the formation of Mg2Si phase. The addition of 2.5 wt.% SiO2 enhanced hardness while the stiffness values remained the same. The results of potentiodynamic polarization tests revealed an improved corrosion resistance of Mg reinforced with SiO2 nanoparticles. Thus, this work is an attempt to understand the fabrication (dissociation of silica into Mg2Si in presence of Mg) and corrosion properties of silica reinforced magnesium composites with those of pure magnesium targeting biomedical applications.