The invention relates to: a process for producing a poly(phenylene ether) resin composition which comprises (A) a poly(phenylene ether) and (B) a styrene resin and in which the styrene resin (B) is a styrene resin comprising a rubber-modified polystyrene containing a polybutadiene having 90% or higher cis-1,4 bonds, the process comprising a first step in which the poly(phenylene ether) (A) is melt-kneaded together with (B1) part or all of the styrene resin which does not include any rubber-modified polystyrene containing an unhydrogenated polybutadiene and a subsequent second step in which the remaining styrene resin including (B2) a rubber-modified polystyrene containing a polybutadiene having 90% or higher cis-1,4 bonds is melt-kneaded; and a poly(phenylene ether) resin composition obtained by the process. According to the invention, a modified PPE can be stably supplied which is free from various appearance failures such as black foreign particles, unmelted matter, and color unevenness and is excellent in practical properties such as stability to high-temperature residence, heat exposure resistance, and low-temperature impact resistance, in particular, heat deterioration resistance.