The production of MoO_3 from Sarcheshmeh molybdenite concentrate via a pyro-hydrometallurgical process was studied, The molybdenite concentrate and sodium carbonate were premixed and fused under air atmosphere. Then the fused products were leached in water and the dissolved molybdenum was recovered as ammonium molybdate, The ammonium molybdate was then calcined to produce molybdic oxide. At the fusion stage, the effect of the mass ratio of carbonate to sulfide on the reaction products and the solubility of the products was investigated The results show that during the fusion, sodium molybdate and sodium sulfate are the final reactum products and sodium sulfide is detected as an intermediate reaction product. By melting at 850℃ with 5wt% excess carbonate, the maximum solubility of the products is obtained, The molybdenum is recovered from the solutions as ammonium molybdate.