Nafion-titanate nanotube composites were investigated as electrolytes for proton exchange membrane fuel cells (PEMFCs) operating at high temperature T. With the addition of 5-15 wt % of nanotubes to the ionomer, PEMFC performance can be significantly sustained for T up to 130 degrees C. The polarization curves of PEMFCs using the composite electrolytes reflect a competing effect between an increase in water uptake due to the extremely large surface area of the nanotubes and a decrease in proton conductivity of the composites. (c) 2007 The Electrochemical Society.