A series of novel wholly aromatic sulfonated poly(arylene ether) copolymers containing sulfonic acid groups on the pendants [SC-SPAE, i.e., side-chain-type sulfonated poly(arylene ether)] were prepared by direct copolymerization Of sulfonated monomer [sodium 4-(4-(2,6-difluorobenzoyl)phenoxy) benzenesufonate (SDFBS)I, 4,4'-dichlorodiphenyl sulfone (DCDPS), and 4,4'-dillydroxyldiphenylether (DHDPE). The sulfonate degree (DS) of the copolymers was readily controlled by adjusting the feed ratio of SDFBS to DCDPS. Structures of the sulfonated copolymers were confirmed by FT-IR and NMR. Tough and flexible films of the wholly aromatic copolymers with good thermal and oxidative stability were obtained by solvent cast process in N,N-dimethylacetamide (DMAc) Solution. The films of these side-chain-type copolymers show good dimensional stability, and their water uptake and swelling ratios at high temperature are lower than those of the main-chain-type sulfonated poly(arylene ether) with similar ion exchange capacity (IEC) value. Proton conductivities of the copolymers with high sulfonate degree (DS > 0.7) are higher than 10(-2) S/cm and increase gradually with increasing temperature. At 100 degrees C, the conductivities of SC-SPAE90 (DS = 0.9, IEC = 1.61 mmol g(-1)) and SC-SPAE100 (DS = 1.0, IEC = 1.74 mmol g(-1)) reach 0.12 and 0.14 S/cm, respectively, comparable to that of Nafion117 (0.14 S/cm).