In this work, we prepared NH4PO3/MO2 (M=Si, Ti) composite materials with various amounts of Ti02 using a sol-gel method, which are potential for application as electrolytes for intermediate temperature fuel cells (150-250oQ. The effect of the amount of Ti02 on the conductivities of the composite was investigated systematically by an impedance spectroscopy within the temperature range of 50-275 oC under different atmospheres. The composite SiTi010APP(10mol%Ti02) showed high proton conductivity, 0.001 -0.043 S cm-1 at 150-250'C. The maximum conductivities are 0.043 S cm-1 at 225 IC under humid H2 and 0.0085 S cm-1 at 175 oC under humid air, respectively. A thermogravi metric analysis showed the composite had high thermal stability below 3001C. Moreover, it was found that the microstructure has significant effect on the conductivity of the composites at higher temperature. (c) 2008 Elsevier Ltd. All rights reserved.