The first hydrothermal synthesis of an Al-rich alluaudite-type compound, namely disodium dimanganese aluminium tris(phosphate), which has been obtained at 1073 K and 0.1 GPa starting from the composition Na2Mn2Al(PO4)3, is reported. The crystal structure, which has been refined in the monoclinic C2/c space group, is identical to that of natural alluaudite. The structure consists of kinked chains of edge-sharing M1 and M2 octahedra, which contain Mn2+ and Al3+ ions. The chains are stacked parallel to {101} and are connected in the b direction by the P1 and P2 tetrahedra. These interconnected chains produce channels parallel to c, which contain the large A1 and A2' sites occupied by Na+ and Mn2+ ions.