The environmental and accelerated photodegradation of two polypropylene (PP) films (high and low crystallinity) were investigated. FT-IR measurements coupled with derivatization reactions (NO and SF4), elongation at break tests and gel permeation chromatography technique were used to monitor the degree of oxidation during the UV exposure. No stoichiometry changes were observed under both UV conditions for the PP films. The dominant photoproduct, i.e., ketone, was suggested to be produced from peroxy radicals. The low concentration of tert-alcohol detected questioned the validity of its formation from hydroperoxide decomposition as suggested by several authors. Under natural exposure, the effect of degradation on mechanical property was different for high and low PP. High PP was useless after a short exposure time; low PP retained its physical property for st longer period of time. In the latter case, the analysis of the changes in elongation at break, the polydispersity P = M-w/M-n, the number of chain scissions N-t, and the kinetic accumulation of photoproducts provided strong indications on the mechanisms of acid and ester production and shed some Light on the competition between crosslinking and chain scission reactions. The estimated acceleration factors were 7.5 and 8.5 for high and low PP, respectively, values that were much lower than those obtained for linear low-density polyethylene.