Abstract: A free-flowing silicone polymer powder, said powder having an average particle size of 1 to 1000 microns and being prepared by mixing a polydiorganosiloxane with a silica filler, and a phosphorus-based fire retardant compound are uniformly dispersed in an organic resin using conventional equipment, such as a single screw extruder. The resulting resin composition shows a significant improvement in fire retardancy but does not exhibit the severe deterioration of impact resistance incurred when the resin is modified with only phosphorus-based fire retardant.