A resin composition comprising a polyphenylene ether having, on the average, 0.01 to 10 terminal structures of the formula (1): ##STR1## wherein R.sub.1 to R.sub.5 are each hydrogen, halogen, a substituted or unsubstituted alkyl, alkenyl or alkynyl group, or a substituted or unsubstituted aryl group, R.sub.6 is a substituted or unsubstituted alkylene group, and R.sub.7 to R.sub.11 are each hydrogen, halogen, an alkyl group, an alkoxy group, a phenyl group, a phenoxy group, a nitro group or a cyano group per 100 phenylene ether units, and a primary aliphatic monoamine having an aromatic substituent, which composition has good thermal stability.