Polymer electrolyte fuel cell (PEFC) systems targeting applications to transfer vehicles for short-term missions and larger spacecraft in the future are being developed at NASDA. First, we designed and manufactured a system with a 100W class fuel cell. Through our tests, we found that a humidifier is not necessary when using pure hydrogen and oxygen supplied from opposite directions. In a closed simulated environment, the tests could also demonstrate the stable operation of the fuel cell system where the oxygen was recycled and the hydrogen stream was dead-ended.