This study was conducted to investigate the effects of applying methods and amount of ammonium polyphosphate (0, 2 and 4 wt%) on fire retardancy and mechanical properties of wood flour/polypropylene composites. The results showed that addition of fire retardant improved the mechanical properties such as tensile and flexural strengths and fire retardancy of composites. But by increasing of fire retardant impact strength decreased. The scanning electron microscopy observation on the fracture surface of the composites indicated that fire retardant had a uniform dispersion in the wood flour/PP composites. The observations showed that saturation of wood flour with fire retardant had a positive effect on mechanical properties and fire retardancy.