Abstract. Wood and natural fiber reinforced plastic composites are established for several fields like decking, transportation and automotive applications. In the last decade, extensive researches were conducted to improve the mechanical properties, such as incorporating additives like maleic anhydride grafted polypropylene (MAH-PP). The major challenge is to keep the properties in face of the environmental influence the parts are exposed to. Therefore it's necessary to find the hardest impact factor concerning the mechanical properties. Water absorption (static and cyclic) of the composites was examined at two different temperatures (23, 50°C). A correlation between duration, kind of conditioning, temperature and modification was established. The results indicate that the coupling agent MAH-PP improved significantly the water resistance of the wood plastic composites under climatic conditions and higher temperature accelerated the rate of water absorption of the composites. The decrease of mechanical properties related to cyclic conditions is partially reversible and therefore the cyclic exposition shows less effects compared to static conditions.