A transparent and flexible composite membrane with homogeneously distributed silica was prepared by one-pot synthesis of perfluorosulfonic ionomer (PFSI) and commercial silica sol. The PFSI dissolved in N,N-dimethylformamide (DNIF) was used instead of aqueous/alcohol solution to increase the co-solubility between silica sol and PFSI. The conductivity of the composite membrane was doubled than that of the host polymer membrane to a value of 0.111 S cm(-1). The single fuel cell testing showed that the fuel cell with homogeneous composite membrane gave much better performance under the operation conditions without external humidification compared to that of host polymer membrane and NR112 membrane. It is believed that the increase in the homogeneity of the composite membrane is benefited from the increased co-solubility between silica sol and PFSI in DMF. It can be concluded that the homogeneous distribution of the components is crucial for the better performance. (c) 2006 Elsevier Ltd. All rights reserved.