Oxidative stabilization of petroleum derived mesophase pitch fiber under increasing temperature conditions was simulated through the use of a kinetic model in which the mass transfer of the oxygen molecules and the autoxidation reaction with the active site in the fiber were taken into account. Temperature dependence of physicochemical parameters such as the effective diffusivity of oxygen molecules in the fiber, the reaction rate constant and the gas-solid equilibrium coefficient of oxygen molecules, were introduced into the mathematical model. The validity of the kinetic model and the numerical calculations was ascertained by comparison of the theoretical values forthe outlet concentration of oxygen gas and the rate of oxygen consumption by the fibers with experimental values. The stabilization reaction was completed prior to the entire consumption of activesites in the fiber, and fixed oxygen was considered to be non-uniformly distributed in the direction of the fiber radius.