Fuel cells, which have seen remarkable progress in the last decade, are being developed for transportation, as well as for both stationary and portable power generation. For residential applications, the fuel cells with the largest market segment are the proton exchange membrane fuel cells, which are suitable for small utilities since they offer many advantages: high power density, small footprint, low operating temperature, fast start-up and shutdown, low emissions, and quiet operation. On the other hand, polymer electrolyte membrane (PEM) fuel cells require high purity hydrogen as fuel. Currently, the infrastructure for the distribution of hydrogen is almost nonexistent. In order to use PEM fuel cell technology on a large scale, it is necessary to feed them with conventional fuel such as natural gas, liquefied petroleum gas, gasoline or methanol to generate hydrogen in situ. This study aims to predict the performance of a PEM fuel cell integrated with a hydrogen generator based on steam reforming process. This integrated power unit will be able to provide clean, continuous power for on-site residential or light commercial applications. A precommercial natural gas fuel processor has been chosen as hydrogen generator. This fuel processor contains all the elements—desulphurizer, steam reformer, shift converter, preferential oxidation (PROX) reactor, steam generator, burner, and heat exchanger—in one package. The reforming system has been modeled with the ASPEN PLUS code. The model has a modular structure in order to allow performance analysis, component by component. Experimental investigations have been conducted to evaluate the performance of the fuel cell fed with the reformate gas, as produced by the reformer. The performance of the integrated system reformer/fuel cell has been evaluated both using the numerical results of the reformer modeling and the experimental data of the PEM fuel cell.