A kinetic study has been made of the absorption of oxygen by unannealed and annealed oriented films of isotactic PP with different drawing ratios at 130°, the oxygen pressures being 150 and 600 torr. In the case of the unannealed samples the induction period in the oxidation process grows longer as the drawing ratio increases, while the rate of oxidation in the autocatalytic region is reduced. The initial rate of oxidation is reduced in line with reductions in the average conformational mobility of amorphous phase chain segments characterized by the spin-probe mobility, by the rigidity of the samples and by the magnitude of shrinkage stresses. The annealing of stresses or chemical relaxation of the latter during the oxidation process lead to a higher initial rate of oxidation, and to a smoothing out of differences between samples with different drawing ratios.