The synthesis of magnesium silicon nitride (MgSiN2) by direct nitridation of a Si/Mg2Si/Mg/Si3N4 powder mixture is described. A nucleation period at 550degreesC and stepwise heat-treatment schedule up to 1350degreesC was adopted for the synthesis of MgSiN2 powder, based on TG-DTA measurements. The influence of the ratio of constituents on the final phase composition also has been studied. The content of magnesium and silicon in the starting powder should fulfill the conditions Mg2Si/Mg greater than or equal to 3 and Si3N4/Si-tot greater than or equal to 0.5 to obtain single-phase MgSiN2. The silicon particle size of <0.5 mum is preferable to decrease the time of nitridation. The oxygen content of as-synthesized powders is in the range 0.9-1.2 wt%. However, the oxygen content of MgSiN2 powder decreases further by the addition of 2 wt% CaF2 or 0.75 wt% carbon and reaching the lowest value of 0.45 wt% oxygen after carbothermal reduction in an alumina-tube furnace.