Based on thermodynamic analysis, the reduction and volatilization of magnesium in ludwigite were studied using carbothermal reduction-nitridation method. The experimental result show that the total mass loss rate of samples increase with temperature rising, which the maximum is 52.88 wt% in the range from 1440°C to 1470°C. Magnesia in ludwigite was reduced and volatilized as gaseous magnesium vapour in the process of carbothermal reduction, and its mass loss rate go up to 98.138%. Part of the volatilized matter formed white powder deposited at the opening of furnace tube and adhered to tube wall together with boride/silicon volatilized. It was proved that there is volatilization of MgO from ludwigite in the process of carbothermal reduction-nitridation.