Abstract: Iron-based sulfides self-lubricating alloys with different contents of molybdenum were prepared with a medium-frequency induction furnace. The evolution of molybdenum sulfide in these alloys was studied by scanning electron microscope and X-ray diffractometer. The results showed that only FeS formed in the alloy and Mo presented as Fe₃Mo₂ with a Mo mass fraction of 1.5%. When the mass fraction of Mo was 6.5%, no MoS₂ formed, and Mo still presented as Fe₃Mo₂. When the mass fraction of Mo was 11%, only a small quantity of MoS_x could form and great majority of Mo and Fe formed the compound Fe₃Mo₂. MoS_x formed remarkably when the mass fraction of Mo was up to 19.5%. It is difficult for molybdenum sulfides to be formed with Mo mass fractions less than 10%. Annealing treatment is favorable for MoS_x formation, but no pure MoS_x was found in the above alloys. MoS_x is a metastable phase formed through the decomposition of Fe-Mo-S compounds. V, Nb and Ti, which are used to decrease grain size in the alloys, are disadvantageous for the formation of molybdenum sulfides due to their strong bonding force to sulfur. Aluminum used as deoxidant should be added in a small amount.