The crystal structure of tripotassium pentairon hexaphosphate has been determined by single-crystal X-ray diffraction. The structure contains one Fe atom on a center of symmetry, one K, two Fe and two P atoms on twofold axes, and one Fe, two P and one K atom in general positions. The K(3)Fe(5)(PO(4))(6) structure consists of a complex three-dimensional framework of corner-sharing between iron polyhedra, and corner- and edge-sharing between PO(4) tetrahedra and iron polyhedra (FeO(5) and FeO(6)). This linkage between iron and phosphorus forms intersecting channels containing the K atoms.