A novel photocatalyst consisting of an intercalated perovskite H1-2xPtxLaNb2O7 was fabricated by ion, exchange. Synchrotron X-ray diffraction and X-ray photoelectron spectroscopy results confirmed that Pt2+ exists within the interlayer space of the layered perovskite: H1-2xPtxLaNb2O7 composed of layered niobate perovskite. and intercalated Pt2+ completely degraded a 20 ppm phenol solution in 3 h under irradiation by Xe light, which exhibits photocatalytic activity superior to those of RbLaNb2O7, Pt-deposited RbLaNb2O7, and HLaNb2O7. From first-principles density functional theory simulation, high photocatalytic activity Of H1-2xPtxLaNb2O7 is attributed to the emergence of a new O 2p-Pt 5d hybridized band on top of the valence band.