By immersing Nafion membrane into dopamine aqueous solution under mild conditions, a series of modified Nafion membranes for the application in direct methanol fuel cell (DMFC) were fabricated. High resolution scanning electron microscope and Fourier transform infrared spectra characterization revealed that a dense nano-layer around 50 nm was formed and adhered tightly to Nafion surface. Small-angle X-ray scattering, wide X-ray diffractometer and positron annihilation lifetime spectroscopy analysis implied that the microstructure such as phase-separated structure and ion-cluster channel of Nafion layer was slightly changed after surface modification. The influence of modification conditions including pH value, dopamine concentration and immersing time upon membrane performance was investigated. Due to the effective reduction of methanol dissolution and enhancement of methanol diffusion resistance, the methanol crossover of the modified membranes was dramatically Suppressed by about 79% from 3.14 x 10(-6) to about 0.65 x 10(-6) cm(2) s(-1). Meanwhile, the proton conductivity of the modified membranes was slightly decreased to be around 0.06 S cm(-1). Consequently, the comprehensive performance of the modified membranes was improved by about five times. These results hinted the application promises of such modified Nafion membranes in DMFC. (C) 2009 Elsevier B.V. All rights reserved.