Sol-gel-derived P2O5-SiO2 glasses were investigated to prepare high proton conductors for fuel cell electrolyte. Glasses with a pore size of 2-30 nm diam were prepared using Si(OC2H5)(4), colloidal silica, PO(OCH3)(3), H3PO4, and POCl3, the pore properties of which were discussed to relate with the water absorption and proton conduction from conductivity measurements and relaxation of proton transfer. In the glasses with pores larger than 10 nm, high humidity is needed to absorb the water in pores, resulting in low proton conductivity. As the pore size decreases, the pores are filled with the water molecules at low humidity, which act to form the pathways of the proton transfer. The P2O5-SiO2 glasses having 2 nm diam pores exhibited high conductivity of similar to100 mS/ cm at 50 degreesC and above 50% relative humidity. (C) 2004 The Electrochemical Society.