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The effects of the rotational speed (0–10 rpm) and temperature (550–650 °C) of rotary kiln drums on the oxidation roasting of molybdenite (MoS2) concentrate was investigated in this study. Computational predictions indicated that production of MoO2 was more favorable than that of MoO3 up to a certain stage of the oxidation roasting process, after which MoO3 is produced through the consumption of MoO2. Thus, understanding the MoS2–MoO2–MoO3 relationship and its equilibrium is important. A drum rotational speed > 5 rpm significantly increased the S reduction rate and considerably decreased the S content at 60 min to < approx. 5 %. Additionally, the S content at 60 min decreased with decreasing the temperature from 650 to 550 °C due to the MoS2 concentrate exothermic reaction during oxidation roasting. The MoS2 to MoxOy (≈ MoO2+MoO3) conversion rate (%) was generally proportional to the rotational speed and reaction duration. X-ray diffraction analysis indicated that 5–10 rpm and 550–600 °C yielded a higher experimental conversion rate (97–98 %). Furthermore, the MoO2 and MoO3 conversions were separately quantified. Agglomeration was more pronounced without drum rotation and at higher temperatures. Analysis of the reaction kinetics using the unreacted-core model indicated that diffusion through the gas film layer is supported by the 20.9 kJ/mol activation energy obtained from the Arrhenius plot. Consequently, an appropriate drum rotational speed at a relatively low temperature is a prerequisite for producing MoO3 through the oxidation roasting of MoS2 concentrates in a rotary kiln.