Abstract: A novel thermoplastic resin composition excellent in heat resistance, mechanical properties and processability is provided which comprises a composition containing (A) a dispersing phase of polyphenylene ether obtained by oxidation polymerization of at least one phenol compound represented by the formula: ##STR1## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 each represents a hydrogen atom, a halogen atom or a substituted or unsubstituted hydrocarbon residue and at least one of them is a hydrogen atom and (B) a crystalline thermoplastic resin matrix phase and (C) a mutual compatibilizer compatible with (A) and/or (B), an average particle diameter in said dispersing phase having of 0.01-10.mu..