Hydrogen permeation of thin Pd-25Ag membranes with the thickness down to 1.2 μm was investigated by conventional gas permeation method within the temperature range of 473–673 K. The thin Pd-25Ag membranes with the thickness down to 51 μm were prepared by cold rolling method. The 1.2 μm-thick Pd-25Ag membrane was prepared by microsystem technology. The hydrogen permeation of the prepared Pd-25Ag membranes was independent of the membrane thickness until down to 51 μm. The 51 μm-thick Pd-25Ag membrane had the hydrogen permeability lower by 60% than that of the bulk Pd-25Ag metal. It mainly resulted from slow surface reaction and lower hydrogen solubility near the surface of the 51 μm-thick Pd-25Ag membrane. The hydrogen permeability of the 1.2 μm-thick Pd-25Ag membrane was one order lower than that of bulk Pd-25Ag metal because the hydrogen permeation was mainly limited by surface reaction. However, literature review indicated that the microfabricated 1.2 μm-thick Pd-25Ag membrane had the hydrogen permeability superior to those conventional Pd-25Ag membranes supported by porous materials, suggesting attractive advantages of the microsystem technology in hydrogen-separation membrane applications.