Since 2000, a technical program was developed to convert biogas into hydrogen-rich gas, and to demonstrate the possibility of applying the acquired hydrogenous gas to the polymer electrolyte fuel cell (PEFC). The gas conversion was accomplished in two steps, successively, in a desulfurizer that removes the hydrogen sulfide in biogas and in a hydrogen-rich gas producer that converts the desulfurized biogas into hydrogen-rich gas containing CO less than the PEFC-tolerable value of 10 ppm. The gas producer consisted of four catalytic reactors, in succession, a steam reformer, two water-gas-shift reactors, and a selective CO oxidizer. Determining the necessary conditions for all such reactors and the applicability of the produced hydrogen-rich gas to a 50-watt model PEFC stack is examined. Experiments were conducted using clean model biogas over commercial catalysts. A successful production of the PEFC-usable hydrogen-rich gas was fulfilled, and the gas showed a composition of about 70 vol. % H-2, 30 vol. % CO2, and residual CH4 (<1.0 vol. %). Directly applying the gas to the downstream model PEFC stack generated stable powers higher than 50 watts, provided the equivalent hydrogen feed was sufficient. Nonetheless, the CO2 in the gas obviously reduced the stack performance. Compared to the case running on pure hydrogen, the stack exhibited not only a lower voltage (power) at a given current, but also a smaller limit current that restricts the maximal output from the stack at each specified hydrogen feed rate. (C) 2004 American Institute of Chemical Engineers.