Electrochemical pumping of hydrogen through high temperature-type proton-conducting solid electrolytes has been studied. The effect of water vapor introduced to the cathode on the hydrogen-pumping capacity of the SrCe0.95Yb0.05O3-alpha proton conductor cell was investigated in the present study. The pumping capacity of the cell was greatly enhanced when water vapor was introduced to the cathode, The water vapor was consumed at the cathode due to the minor partial oxide ionic conduction in the electrolyte. The role of the water vapor at the cathode in the hydrogen pump is discussed.