To obtain a resin composition excellent in hot water resistance and durability and provide a pump part comprising the resin composition.

This resin composition excellent in heat resistance is obtained by compounding (a) 50-95 pts.wt. resin composition obtained by substituting a part or all of a polyphenylene ether-based resin with a modified polyphenylene ether-based resin modified with an unsaturated carboxylic acid or its functional derivative in a polyphenylene ether-based resin or a resin composition comprising the polyphenylene ether-based resin and an aromatic vinyl compound-based polymer with (b) 5 50 pts.wt. pseudo random copolymer of an α-olefin with an aromatic monovinylidene compound and (c) 10-200 pts.wt. inorganic filler, with the proviso that pts.wt. is a value based on 100 pts.wt. total amount of component (a) and component (b). This pump part is composed of a resin composition.