X-ray photoelectron spectroscopy (XPS) was used to study the hydrolytic aging of polypropylene according to the pHs of degrading buffer solutions and the time of aging. The study was concentrated over periods of 3, 6, and 9 months for values of pH close to the real environments of use of the material (pH of 6, 7, and 8). The polypropylene underwent an oxidation of its polymeric matrix, independently of the range of pH values, by the production of C-OH, C=O, and O=C-O groups. These chemical functions were observed in high resolution XPS spectra around C1s and O1s peaks. Beginning with these results and from mechanisms of (photochemical, thermal, and others) aging proposed in the literature, it was then possible to propose mechanisms of hydrolytic ageing of polypropylene. (C) 2004 Wiley Periodicals, Inc.