A reformate fuel cell system is one of the most promising power generation systems in the future. Thus, it is important to understand the behaviour of a fuel cell in reformate gas. In this study, the fuel cell performance in the simulated reformate gas is studied. From this study, it is concluded that the fuel cell performance is influenced by the operational current, nitrogen concentration and the carbon monoxide concentration for a proton exchange membrane fuel cell which uses Pt/Ru as the anodic catalyst. A voltage fluctuation phenomenon at high carbon monoxide concentrations is observed and discussed in this study.