Series of new copoly(arylene ether)s containing naphthalene or naphthalene/1,3,4-oxadiazole units have been obtained by polycondensation in solution starting from the following systems of monomers: 1,5 or 2,6-bis(4-fluorobenzenesulfonyl) naphthalene 2,6-bis(4-fluorobenzoyl)naphthalene, 1,5 or 2,6-bis(4-fluorobenzen sulfonyl)naphthalene 2,2'-(oxydi-4,1-phenylene)bis[5-(4-fluorophenyl)-1,3,4oxadiazole] and 2,6 bis-(4 fluorobenzoyl)naphthalene/2,2'-(oxydi-4,1-phenylene)bis [5-(4-fluorophenyl)-1,3,4-oxadiazole]. Hydroquinone and 4,4'dihydroxy benzophenone have been used as aromatic dihydroxy compounds. The copolymers, obtained in quantitative yields, possessed inherent viscosities in the range 0.28-0.58 dl g(-1), had good thermal stability (10% weight loss temperatures were above 460degreesC both in nitrogen and air) and high glass transition temperatures (in the range 190-210degreesC). They have been characterized by infrared analyses, GPC and wide-angle X-ray diffraction. The copolymer property-structure relationships were studied and the properties have been compared with those of the corresponding homopolymers.