Magnesium silicon nitride (MgSiN2) nanoparticles have been synthesized by using magnesium silicide (Mg2Si), sodium azide (NaN3) and sulfur as starting materials in a stainless steel autoclave at relatively low temperature. X-ray powder diffraction patterns indicate the obtained products are orthorhombic phase MgSiN2. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images reveal that the average size of product is 40 nm. The oxidation resistance of the obtained MgSiN2 nanoparticles has been investigated.