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In the title compound, K9Al3(PO4)6, the anionic substructure is built of interlinked [PO4] and [AlO4] tetrahedra. Each O atom of the [AlO4] tetrahedron is common to a positionally different [PO4] tetrahedron; thus, each [AlO4] tetrahedron is surrounded by four positionally different [PO4] tetrahedra. On the other hand, each [PO4] tetrahedron shares its two O atoms with two positionally different [AlO4] tetrahedra; the other two phosphate O atoms are terminal ones coordinated by K atoms. The terminal O atoms are usually closer to the K atoms than the bridging O atoms between the [AlO4] and [PO4] tetrahedra. There are nine symmetry-independent K atoms in the structure. The coordination numbers of the K atoms are 6 or 7 or 8 up to a distance of 3.31 Å. There are channels in the anionic substructure oriented along the [10overline{1}] direction that are filled by K atoms.