Photon-stimulated desorptions from aluminum surfaces was studied. Aluminum samples, following exposure to water vapor, were irradiated by synchrotron light with a critical photon energy of 2.1 keV. The signal corresponding to H2O gas exponentially decreased during irradiation. Experiments were performed under various conditions of target bias, sample temperature, photon flux, and photon dose to clarify the H2O PSD behavior. The experimental system, results, and discussions are described.