A description is given of a fuel-cell power-supply for mobile phones that operates at room temperature and ambient pressure using liquid methanol and ambient air. The unit is a hybrid system in which a direct methanol fuel-cell (DMFC) and a back-up battery are connected in parallel to meet the power requirements of mobile phones. Electrochemical catalysts for the anode and the cathode of the DMFC are synthesized and Nafion-115 is used as the electrolyte. A 2M methanol solution is filled in the feed reservoir, and the cathode is exposed to ambient air. Eight unit cells, each having 9cm2 of active area, are connected in series in order to raise the output voltage to 2.5–3.9V, which is the typical voltage range for most mobile phones. Also, to simulate the practical application, an electric circuit is included to increase the output voltage of the back-up battery to repeat the charge–discharge cycle. During talk mode, the DMFC supplies 10–50% of the required power and the back-up battery supplies the remainder. In standby mode, the DMFC covers 100% of the required power and charges the back-up battery.