The development of a direct methanol fuel cell based on composite polysulfone membranes modified with silica filler is reported. The synthesis of sulfonate polysulfone samples was carried out by a mild sulfonation process using trimethyl silyl chlorosulfonate as sulfonating agent. Composites membranes with 5 wt% of silica filler were prepared and characterized. A composite membrane tested in direct methanol/oxygen fuel cell gave a maximum power density of about 180 mW cm(-2) at 120 degrees C.