In this work, the effect of vacuum ultraviolet (VUV) exposure on the time-dependent dielectric breakdown (TDDB) properties of porous low-k films was investigated. Synchrotron irradiation was used to simulate the VUV photon irradiation from processing plasmas without any particle flux. The synchrotron flux varies with the wavelength, so the irradiation time was chosen to produce the same fluence at various photon energies. The deterioration of TDDB and generation of negative mobile charge were observed in the film after exposure to the VUV photons with 9 eV or higher energy. These effects were not observed in the films exposed with 7-eV photon energies or less. The creation of paramagnetic defects was observed with the ESR measurement and believed to be the reason for TDDB degradation. Depletion of carbon and breakage and rearrangement of the Si-O-Si structure were observed and believed to be the reason for mobile charge generation and the change in TDDB, chemical, and mechanical properties.