Roasting experiments were carried out with pure reagents as raw materials. The self-sintering behaviors of molybdenite (MoS₂) during oxidation were investigated by thermodynamic calculation, XRD, SEM-EDS and high-temperature in situ analysis. The results indicate that the desulfurization efficiency of MoS₂ pellet decreases with the increase of roasting temperature from 600 to 700 °C, owing to the expansion of sintered area. At the very beginning of roasting, sintered layer can be rapidly formed and cover the pellet surface on the windward side, and meanwhile, MoO₂ and Mo₄O₁₁ intensively appear and constitute the sintered layer together with MoO₃. Moreover, it is proven that MoO₃-rich products containing low-valence molybdenum oxides have low melting points, thus easy to be melted during the occurrence of exothermic reaction between MoS₂ and O₂, which leads to the sintering of materials.