The chemiluminescence from stabilized nylon 66 fibers during oxidation above Tghas been studied to determine the activation energies of the initiation, propagation and termination reactions. When oxygen is admitted to a nylon 66 sample heated in an inert atmosphere, a pulse of chemiluminescence is observed corresponding to a nonstationary alkyl peroxy radical concentration in the polymer. The analysis of the decay to the steady state can provide kinetic data for peroxy radical reactions in the induction period of the oxidation and the effect of stabilizers on these reactions.