A series of sulfonated polybenzimidazoles (SPBIs) with varied ion exchange capacities (IECs) have been synthesized by random condensation copolymerization of a new sulfonated dicarboxylic acid monomer 4,6-bis(4-carboxyphenoxy)benzene-1,3-disulfonate (BCPOBDS-Na), 4,4′-dicarboxydiphenyl ether (DCDPE) and 3,3′-diaminobenzidine (DAB) in Eaton's reagent at 140 °C. Most of the SPBIs show good solubility in polar aprotic organic solvents such as dimethylsulfoxide (DMSO) and N,N-dimethylacetamide (DMAc). Thermogravimetric analysis (TGA) reveals that the SPBIs have excellent thermal stability (desulfonation temperatures (on-set) > 370 °C). The SPBI membranes show good mechanical properties of which tensile strength, elongation at break, and storage modulus are in the range of 89–96 MPa, 12–42%, and 2.4–3.1 GPa, respectively. Moreover, the SPBI membranes exhibit phosphoric acid (PA) uptake in the range of 180–240% (w/w) in 85 wt% PA at 50 °C, while high mechanical properties (13–20 MPa) are maintained. The SPBI membrane with 240% (w/w) PA uptake displays fairly high proton conductivity (37.3 mS cm−1) at 0% relative humidity at 170 °C. The fuel cell fabricated with the PA-doped SPBI membrane (PA uptake = 240% (w/w)) displays good performance with the highest output power density of 0.58 W cm−2 at 170 °C with hydrogen–oxygen gases under ambient pressure without external humidification.Research highlights▶ A series of novel sulfonated polybenzimidazoles (SPBIs) have been synthesized from a new sulfonated dicarboxylic acid monomer, disodium 4,6-bis(4-carboxyphenoxy)benzene-1,3-disulfonate. ▶ The phosphoric acid (PA)-doped SPBI-11 membrane shows high mechanical strength (20 MPa) despite the high PA-doping level (240% (w/w)). ▶ The fuel cell fabricated with the PA-doped SPBI-11 membrane exhibits high performance (the highest output power density: 0.58 W cm-2) at 170 °C with hydrogen-oxygen gases under ambient pressure without any gas humidification.