The oxidation of 100 μm stabilised polypropylene films has been studied at 130<space> o C in air, using physico-chemical and mechanical characterisation methods. During the induction period, where no carbonyl build-up is observable by IR spectroscopy, both stabiliser consumption (UV spectrophotometry) and molecular weight decrease (steric exclusion chromatography) can be observed. These structural modifications induce a decrease of fracture properties as determined using the essential work of fracture (EWF) method whereas tensile ultimate elongation does not display significant variations. The results clearly indicate the interest of the EWF method to characterise degradation induced embrittlement of initially ductile polymers. The experimental data gathered in this work bring some new elements of discussion about the problem of spatial heterogeneity of the oxidation process.