Novel wholly aromatic polyesters 8 containing a terphenyl analogue of 1,3,4-thiadiazole (2,5-diphenyl-1,3,4-thiadiazole) in the main chain were synthesized by high-temperature solution polycondensation of a diacyl chloride derivative of 2,5-diphenyl-1,3,4-thiadiazole 6 with four hydroquinones 7 in 1-chloronaphthalene. These polymers 8 are insoluble in most organic solvents and decompose very rapidly above 400 degrees C in air without showing thermotropic liquid crystalline melts.