The influence of different amounts of micro-sized titanium dioxide (anatase crystalline variety) dispersed into a polybenzimidazole membrane has been studied for its use as an electrolyte in high temperature polymer electrolyte membrane fuel cells. All of the membranes were cast from a polymer with the same molecular weight. The membranes were physicochemically and electrochemically characterized. From the membranes studied with different amounts of TiO₂, the membrane that provided the best properties for its use as an electrolyte was the composite one which contained the lowest amount of filler. The composite membrane with 2 weight percent of the filler absorbed larger (absorbed acid: 2.42 g_acid g_membrane ⁻¹) and leached lower (remaining acid: 0.78 g_acid g_membrane ⁻¹) amounts of acid than the other composite and standard one. Because it has the largest acid and water absorption capability, the 2% TiO₂-PBI showed also the highest ionic conductivity (0.043 S cm⁻¹), measured out of the fuel cell. Fuel cell measurements and also stability tests (> 140 h) were made for the composite membrane with 2% of the filler and the results were compared with a standard polybenzimidazole fuel cell. The TiO₂–PBI composite membrane showed the best performance and achieved a power density of 450 mW cm⁻¹ at 175 °C. Moreover, the composite also showed the best stability under our operation conditions. Thus, the slope of the increase in the ohmic resistance of the composite membrane was 0.009 mΩ cm² h⁻¹ and the polarization resistance was 1.17 mΩ cm² h⁻¹ which was two times lower than that of the standard membrane. The benefit of inorganic filler introduction when the fuel cell operates at high temperature has been highlighted.