[en] We obtain a four-photon polarization-entangled state with a visibility as high as (95.35±0.45)% directly from a single down-conversion source. A success probability of (81.54±1.38)% is observed by applying this entangled state to realize a four-party quantum communication complexity scenario, which comfortably surpasses the classical limit of 50%. As a comparison, two Einstein-Podolsky-Rosen pairs are shown to implement the scenario with a success probability of (73.89±1.33)%. This four-photon state can also be used to fulfill decoherence-free quantum information processing and other advanced quantum communication schemes