In this study, single cell performance of DMFC has been investigated under air-breathing and passive operation conditions. Air-breathing and passive DMFC has been expected to be easily applied to electric power sources, because it is operated without feeding fuel and oxidant by force under a room temperature and atmospheric pressure. And it is possible to make a small size fuel cell with simple operating system for portable electric equipment. In this study, a carbon paper for diffusion layer of DMFC was pretreated in order to control the pore geometry and the physical properties, Pretreated diffusion layer was fabricated by applying RF magnetron sputter0deposited Au on the surface of the carbon paper in argon atmosphere. By the experimental results, single cell performance of the DMFC using non-treated carbon paper and pretreated carbon paper as diffusion layer was 24.8 mW/cm² and 36.7 mW/cm², respectively. By pretreating diffusion layer, average pore diameter was decreased from 0.29 μm to 0.17 μm and the porosity was changed from 72.35% to 75.27%. Also surface resistance was decreased from 11.57 mΩㆍcm² to 7.07 mΩㆍcm². The highest power density of 36.7 mW/cm² was obtained by sputtering Au on the diffusion layer for 90 min.