The oxidation kinetics of MoO2 to MoO3 was investigated in the temperature range 674-791K and in the oxygen partial pressure range 8.1-30.4 kPa. Weight increase during the reaction was determined by thermogravimetric analysis with a microelectronic microbalance. The reaction is 0.6th-order with respect to oxygen concentration and the activation energy was found to be 148 kJ/mole. The data obtained gave a better understanding of the oxidation kinetics of MoS2. By applying the law of additive reaction times to the data for pellets an equation was derived that relates fractional conversion and time. This equation could be applied in isothermal conditions or to the diffusion of reacting gas through the pores of the product layer in non-isothermal conditions. The temperature rise was a result of the heat of the reaction and was calculated by applying a heat balance to the system. The effects of sintering and crack formation on the fractional conversion were also investigated. The findings should be taken into account when designing equipment and choosing operational conditions for the roasting of MoS2.