Improvements in the CO tolerance of the anode has been studied with the objective of developing PEFC modules operated with reformed gas. The CO tolerance of the Pt-Ru alloy anode was improved by reducing its thickness from 40 mu m to 20 mu m Maintaining a saturated steam pressure of the fuel cell anode gas outlet is expected to decrease the influence of CO poisoning. When keeping sufficient water content in the feed fuel, it was established that the cell performance was stable over a wide range of air-humidification conditions. Successful operation was achieved with a 1 kW class system utilizing the improved GO-tolerant anode and fuel processor. An output power of 1.1 kW (average cell voltage: 0.62 V) was achieved at the current density of 0.3 A/cm(2).