Effect of anode diffusion layer over the performance of the liquid feed direct methanol fuel cell has been studied by AC impedance spectroscopy. The anode employed comprises of the catalyst layer and diffusion layer. The latter comprises of backing layer and catalyst-supporting layer. The supporting layer is present in between the backing layer and the catalyst layer. The composition of the supporting layer is optimized based on the information obtained from polarization and AC impedance measurements. Among the three types of carbons (Black pearl 2000, Vulcan XC-72, Shawinigan acetylene black), Black pearls 2000 is found to be the ideal type of carbon used in the supporting layer. The optimized loading compositions of carbon, Nafion and PTFE in the supporting layer are reported to be 3 mg cm(-2), 10 wt%, and 0 wt%, respectively. These values are rationalized on the basis of the transport of methanol and carbon dioxide and the crossover of methanol from the anode to the cathode. Copyright (c) 2006 John Wiley & Sons, Ltd.