PURPOSE: To obtain functionalized polyphenylene ether useful for solubilizing polyphenylene ether and polyamide by bringing polyphenylene ether into contact with a salicylic acid/dicarboxylic acid copolymer under reaction conditions.

CONSTITUTION: A copolymer represented by formula II (wherein R is a stable group such that an intermolecular anhydride is not formed and x, y and n are 1 or more) (B) obtained by reacting salicylic acid and dicarboxylic acid (pref., isophthalic acid) in a ratio of (1:3)-(3:1) pref., 1:1 is brought into contact with polyphenylene ether represented by formula I (wherein Q1 is halogen, primary or secondary lower alkyl phenyl, etc.; and Q2 is H, halogen or primary or secondary lower alkyl, etc.), [pref., poly(2,6-dimethyl-1,4-phenylene either] (A) within a range of 1-10% by wt. of the component A under reaction conditions, pref., under extrusion conditions to obtain polyphenylene ether having a terminal group represented by formula III (Z is H or COCH3).