The aim of the work was to prove the possibility of wood modification by the mixture of thermoplastic and thermohardening polymers. As thermoplastic polymers polyethylene, polypropylene and vinyl polychloride were applied. A thermohardening polymer constituted phenolo-formaldehyde resin. The composite was obtained by hot pressure of the comminuted birch wood of the size of particles varying between 5-25 mm, with the mixture of polymers. It forms, moreover, on the surface of wood particles a thin layer. The affinity of this polymer both to wood and thermoplastic polymer improves the adhesion between polyneric and lignous phase of the composite and affects positively its properties. Such a role of the thermohardening resin has veen proved also by the analysis of the spectra of the composite obtained in IR.