A carbon nanotubes (CNTs) reinforced Nafion composite membrane for the H-2/O-2 fuel cell was developed. CNTs/Nafion composite membrane, in which CNTs were dispersed uniformly, was prepared by solution-casting. CNTs reinforced membranes, with the addition of a small amount of CNTs (1 wt %), showed excellent mechanical strength. The CNTs/Nafion composite membrane could also decrease dimensional change compared with the commercial Nafion membrane. The performance of the CNTs reinforced composite membrane (50 mu m) was almost the same as the cell prepared with commercial Nafion NRE-212 membrane. (c) 2006 The Electrochemical Society.