The in-depth degradation of unprotected low density polyethylene (LDPE) induced by photooxidation was studied by following the carbonyl content and other by-product groups as well as the retention of mechanical properties as a function of time and distance from the surface. The multilayer slabs were prepared by hot pressing of nine LDPE film layers. Weathering of the samples was performed in a Q.U.V. apparatus running dry at 55 degrees C for different time periods. The carbonyl content, as measured by FTIR spectra, showed a parabolic symmetry around the center layer which was least affected. Oxygen barriers placed on one or both surfaces of the slabs significantly reduced the photooxidation. The retention of mechanical properties followed st similar profile as that of the carbonyl. However, the outermost layers, especially those that were close to the UV-radiation source were slightly more affected. The results of this study lead to the conclusion that photooxidation is autocatalytic and is affected primarily by diffusion of oxygen.