Hydrogen transport from gas to liquid phase (water) through a Pd77Ag23 membrane was investigated, where the hydrogen flux was considerably reduced compared with that from gas to gas phase. The reason of such a significant reduction in the flux was discussed by developing a bubble model as well as a solution model. The bubble model, which was simple and required no fitting parameter, was found to be valid within a limited range. The solution model, including the mass transfer coefficient as a parameter to be estimated, was found to be able to mostly correlate the experimental data in the range of pressure and temperature studied.