Creep behaviour of unmodified and functionally modified thermoplastic-wood fibre composites was studied. For PVC, PE and PP-based composites creep is strongly dependent on the amount of load, time and temperature. A small rise in the temperature above ambient temperature increased creep significantly for PVC-woodfiber composites. Instantaneous creep resistance of woodfibre-filled PP is higher than that of PE-based composites. PP and PE-based wood composites were modified with maleic and maleimide compounds. Maleic or maleimide modification of woodfibre improved transient creep behaviour of PP-woodfibre composite but it did not show practically any effect on instantaneous creep. A mathematical model has been proposed to predict creep behaviour of PVC, Pf an PE-based wood fiber composites.