This paper describes the,development, assembly, and test of a portable PEMFC UPS system (CSIST-50-01). CSIST-50-01 is a fuel cell power generator with a dc/dc converter to supply a clean, stable, and high quality power at 20 Vdc. Under dry H-2/air operating condition, the peak power output is about 80W at 20V, and maximum system efficiency is about 30% at 60W. CSIST-50-01 could function as an uninterruptible power supply (UPS) to be a power generator to prevent electronic devices from power interruption. Performance evaluation proves that CSIST-50-01 has fast power responses. CSIST-50-01 costs US$2739-2779, which could be reduced by mass production. Finally, the system characteristics and specifications are compared with other similar systems such as PowerPEM (R) PS-250 (PlugPower), and A-500 (Phoenixtec power). (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.