PURPOSE: To obtain the title substance soluble in organic solvent and useful as a raw material for a heat-resistant crystalline resin, etc., in high yield, by reacting a 4,4'-dihalodiphenylsulfide with an alkali metal salt of a 4-halophenol in an aprotic polar solvent.

CONSTITUTION: The objective phenylene thioether oligomer having terminal functional groups can be produced by reacting a 4,4'-dihalodiphenylsulfide with an alkali metal salt of a 4-halophenol in an aprotic polar solvent (e.g., N,N- dimethylacetamide) at 170W230°C and reacting the resultant compound of formula I (X4 and X5 are halogen; m is 2W10) with a compound of formula II (Y is NH2, OH, COOR or CN; M is Li, Na or K) in an aprotic polar solvent at 160W230°C for 3W12hr. The compound produced by this process is also useful as a material for improving the moldability of a heat-resistant resin.