This research aims to study the photo-degradation characteristics for zinc oxide (ZnO) nanoparticle filled polypropylene (PP) nanocomposites. By paying attention to the evolution of the carbonyl absorption bands from FTIR analysis, it has been observed that UV irradiation induced significant photo-degradation for unfilled PP. However. with the incorporation of ZnO nanoparticles into the PP matrix, the extent of photodegradation was significantly reduced. This is due to the superior UV light screening effects offered by the ZnO nanoparticles. WAXD measurements showed that beta-form PP crystal had been induced in the PP/ZnO nanocomposites. An interesting observation from this study is that beta-form PP crystal was also induced in unfilled PP due to UV irradiation. UV-irradiation induced degradation caused a significant drop in the ductility for unfilled PP. With the incorporation of ZnO nanoparticles, the ductility, and hence the tensile strength were recovered to some extent. The higher the ZnO particle content, the higher the elongation at break value in the UV irradiation treated nanocomposites. It was also observed that surface cracks were induced by photo-degradation, and the Talysurf surface profile measurements indicate that the severity of the surface cracks were significantly reduced in the ZnO/PP nanocomposites. (c) 2006 Elsevier Ltd. All rights reserved.