Wood Plastic Composites (WPC) have gained much acceptance in both the plastic processing and forest products industries in recent years. As the outdoor applications of WPC become more widespread, the color stability of these products against ultraviolet becomes a concern.The most effective formulation in stabilizing the overall color change was a combination of both high and low molecular weight diesters and a benzotriazole based UVA.Lignin experiences two competitive redox reactions namely oxidation to chromophores (which causes yellowing) and reduction of chromophores to hydroperoxides (which causes photobleaching).ToF-SIMS analysis revealed that High Density Polyethylene (HDPE) undergoes photodegradation according to Norrish Type I reaction after UV exposure. FTIR spectroscopy revealed that the HDPE undergoes two competitive reactions namely chain scission and crosslinking.In the present work, the performance of different photostabilizers was investigated. Furthermore, a reaction mechanism for the changes in surface chemistry of the UV weathered WPC was proposed.