An austenitic stainless steel with a niobium diffusion protective layer is evaluated for bipolar plate of direct methanol fuel cell (DMFC). Corrosion resistance of niobium diffusion modified AISI 304 stainless steel (niobized 304 SS) is investigated in simulated DMFC cathodic environment (0.5 M H2SO4 + 2 ppm HF + 0.1 M methanol solution at 50 degrees C) and anodic environment (0.5 M H2SO4 + 2 ppm HF + (1 M, 10 M and 20 M) methanol solution at 50 degrees C), respectively. Potentiodynamic, potentiostatic as well as electrochemical impedance spectroscopy tests show that, comparing with a bare 304 SS, the corrosion current density of niobized 304 SS is reduced greatly while the polarization resistance is raised in the simulated DMFC cathodic environment. Corrosion tests in the simulated anodic environment are applied to examine the effect of methanol on the corrosion behaviour of niobized 304 SS. It is interesting to find that the niobized 304 SS shows better corrosion resistance in the higher methanol concentration solutions. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights, reserved.