A thermodynamic and kinetics investigation on the oxidation of MoS2 in molybdenite concentrate to MoO2 by water vapor was carried out as part of new process development. The kinetics of the reaction were determined by measuring the weight change of a sample with time in water vapor at temperatures between 700 °C and 1000 °C. The reaction rate followed the shrinking-unreacted-core model under chemical reaction control, which showed activation energy of 102 kJ/mol. In addition, the behavior of rhenium and selenium in molybdenum concentrate during the process was investigated. While most rhenium remained with the molybdenum dioxide during the water vapor oxidation, almost all selenium was volatilized in agreement with thermodynamic analysis.