The photodegradation of isotactic polypropylene (PP) films containing a monoazo pigment and hindered amine light stabilizers (HALS) has been undertaken. PP films were exposed to medium pressure mercury lamp radiation in the laboratory for periods of up to 8 weeks and the degree of degradation (oxidation/ deterioration) was examined using FTIR spectroscopy and differential scanning calorimetry (DSC) as well as by measuring changes in the mechanical properties, contact angle, and density. The results of these measurements indicate that unstabilized PP films degraded after only 240-h irradiation. By adding an organic pigment to PP films along with antioxidant and HALS, the photostability of PP films increased to the 1500-h level. (C) 2008 Wiley Periodicals, Inc.