Single crystals of the title compound, Al2P6O18, were obtained by solid-state reaction. The monoclinic structure is isotypic with its CrIII, GaIII and RuIII analogues and is built up of six-membered phosphate ring anions, P6O18
6−, isolated from each other and further linked by isolated AlO6 octahedra by sharing corners. Each AlO6 octahedron is linked to four P6O18
6− rings. More accurately, two rings are linked through bidentate diphosphate groups attached in the cis-positions to the AlO6 octahedron. The other two rings are linked to the two remaining corners, also in cis-positions of the AlO6 octahedron.