Thermodynamics for reduction of molybdenum oxides by aluminum and silicon were calculated, and the results show that reduction reaction is feasible at a certain temperature region. Compared to the presence of CaO or CaCO 3 , reduction products of molybdenum trioxide with aluminum and silicon at various temperatures were detected by X-ray diffraction (XRD). Results show that molybdenum trioxide is reduced by aluminum or silicon step by step, and the intermediate product is MoO 2 . At 1000°C, molybdenum trioxide could be reduced to metal Mo by aluminum, and in the presence of CaO, metal Mo as the reduction product appears even at 800°C. In contrast, silicon could barely reduce molybdenum trioxide to metal Mo even at 1200°C. In the presence of CaO or CaCO 3 , reducibility of silicon increases significantly, and the reduction products are metal Mo and MoSi 2 . Altogether, CaO or CaCO 3 performs two major roles in reduction process: restraining sublimation of MoO 3 and decreasing the temperature of reducing MoO 3 to metal Mo.