Abstract: A free-flowing silicone rubber powder, having an average particle size of 1 to 1000 microns and prepared by mixing a polydiorganosiloxane with a silica filler, is uniformly dispersed in a poly(phenylene ether) resin using conventional equipment, such as a single screw or, preferably, a twin screw extruder. When employed at relatively low concentrations, such as about 0.2 to 3 parts by weight of powder per 100 parts by weight of resin, a significant improvement in the processability is obtained, while modification at higher levels, such as 5 to 20 parts by weight of powder per 100 parts by weight of the resin results in a resin composition having greatly augmented impact resistance.