Cellulose whiskers (CWs) were explored as effective nanostructures to manipulate the microstructure of Nafion (R) membranes for high-performance fuel cell applications. Electrochemical impedance measurements revealed that not only the proton conductivity of the nanocomposite membranes comprising 5 wt% CWs was remarkably increased, but the higher conductivity was also retained at higher temperatures (> 100 degrees C). Moreover, it was found that the inclusion of CWs into a Nafion (R) matrix provides considerably suppressed methanol permeability. The direct methanol-air single fuel cell test using 5 M methanol solution at 70 degrees C showed a higher maximum power density of 91 mW cm(-2) for the nanocomposite membrane, compared to 28 and 47 mW cm(-2) for unmodified Nafion (R). Hence, CWs could be considered as effective and elegant nanostructures to regulate the ionic microstructure and alleviate critical drawbacks of Nafion membranes for commercial direct methanol fuel cell applications.