PURPOSE: To provide the subject oligomer by reacting dibromobenzene with 4-halo thiophenol alkali metal salt in an aprotic polar solvent, or to provide a functional group-terminated oligomer by further reacting the product with an aromatic mercaptide.

CONSTITUTION: An oligomer of formula I (X1 and X2 are halogen; m is 1W10) is obtained by reacting dibromobenzene with 4-halo thiophenol alkali metal salt in an aprotic polar solvent (e.g., DMF) at 170W230°C for 5W15hr. The obtained oligomer is reacted with a compound of formula II (Y is NH2, OH, CH, etc.; M1 is Li, Na or K) at 160W230°C for 3W12hr to provide an oligomer of formula III. The oligomer is useful as a raw material for crystalline aromatic- poly(thio)ether, -polyamide, -polyimide, -polyester, etc., and also as a moldability- improving agent for heat-resistant resins. The above-mentioned method provides the objective compound in a high yield.