Bio-composites are composite materials using reinforcements and resins of animal or vegetable origins. They are a combination of thermoplastic or thermosetting resins and reinforcements in micro spheres, fibers, woven or non-woven forms. The production technologies are mainly injection and thermos-compression. In recent years, polymer matrix composites have seen their demand grow considerably. This is due to the properties of the new material; The development of these materials based on natural fibers has many advantages due to their biodegradability and their low density. Generally, wood-plastic composites (WPC) are formed through the polymerization of a monomer in the empty pores of solid wood. The role of the polymer matrix is to distribute the charge between the fibers and to ensure their assembly and adhesion. The absorption of water from wood (fibers) is mainly due to the hydroxyl groups (-OH) of cellulose and hemicelluloses; The presence of moisture is a very important factor for the development of microorganisms, especially fungi which are multi-cellular or unicellular eukaryotes. Gloephyllyllum trabeum (brown rot fungus) is the fungal species responsible for the degradation of wood in the wild. Disadvantages of the use of composites in an external environment arise with regard to the vulnerability to water absorption, the possible infestation by Gloephyllyllum trabeum which attack the fibers structure. The combined action of moisture and fungal attack could affect the physical and mechanical properties of this material. However, the application of certain substances (zinc oxide) to the external parts of these could have a positive impact on their resistance to humidity and / or the fungal attack.