A reformed methanol fuel cell system is one of the most practical of all types of fuel cell systems. It is regarded as one of the best candidates for stationary applications, such as residential power generators, uninterruptible power supply systems, power generators for cell base stations, or power generators in outlying areas. In this research, a 1-kW self-sustainable proton exchange membrane fuel cell system with a methanol reformer is designed and tested. The system performance test and in situ stack monitoring show that the system is stable and reliable. During normal operation, the maximum voltage deviation among the individual cells, which is caused by a nonuniform temperature distribution in the proton exchange membrane fuel cell stack, is 25 mV. The peak power output of the system reaches 1.4 kW. The maximum electrical efficiency is 65.2% at a system power of 1 kW. The system is operated at 1 kW for 4 h, during which the decay rate of the stack power is 0.94%. During the stability test, voltage fluctuation occurs in a certain cell because of a flooding phenomenon. A demonstration is also presented in this paper to show the system’s practicability and commercial potential.