The title compound, potassium pentanickel hexaborophosphate tridecahydroxide, was synthesized under hydrothermal conditions from the NiCl(2)-K(3)PO(4)-B(2)O(3)-K(2)CO(3)-H(2)O system. The crystal structure was determined using single-crystal X-ray diffraction at 100 K. The KNi(5)[P(6)B(6)O(23)(OH)(13)] phase is cubic. For the three crystallographically distinct Ni centers, two occupy sites with 3 symmetry, while the third Ni and the K atom are located on 3 sites. The structure is built from alternating borate and phosphate tetrahedra forming 12-membered puckered rings with K(+) ions at the centers. These rings are arranged as in cubic dense sphere packing. A novel feature of the new crystal structure is the presence of linear trimers of face-sharing [NiO(6)] octahedra occupying the octahedral interstices of this sphere packing, and of single [NiO(6)] octahedra in the tetrahedral interstices. All oxygen corners of the Ni octahedra are linked to phosphate or borate tetrahedra of the 12-membered rings to form a mixed anionic framework.