Highly proton-conductive acid-impregnated mesoporous silica gels have been prepared using alkyltrimethylammonium. chlorides with different alkyl chain length as a template and several kinds of protonic acids such as HClO4, H2SO4 and H3PO4 as a proton donor. The specific surface area and pore volume of the mesoporous silica gels increased with an increase in the number of carbon atoms in the alkyl chain. The electric conductivities of all the acid-impregnated mesoporous silica gels also tended to increase with increasing the number of carbon atoms in the alkyl chain in the surfactant. This phenomenon can be ascribed to an increase in the amounts of impregnated acid due to the enlarged pore volume in the mesoporous silica gels. It was found that HClO4 and H2SO4 more effectively enhanced the proton conductivity of the resultant acid-impregnated silica gels than H3PO4. The conductivities of the HClO4- and H2SO4-impregnated mesoporous silica gels obtained were higher than 10(-1) S cm(-1) under 60% relative humidity at 85 degreesC.