The title compounds have been synthesized by a solid state reaction route using a salt flux. Their crystal structures were determined from single crystal X-ray data. NaKAl2O[AsO4](2) crystallizes with the orthorhombic K2Fe2O[AsO4](2)-type, Pnma, a = 8.2368(6) angstrom, b = 5.5228(3) angstrom, c = 17.0160(13) angstrom and Z= 4, whereas Na2KAl3[AsO4](4) crystallizes with the orthorhombic K3Fe3[AsO4](4)-type, Cmce, a = 10.5049(9), b = 20.482(2), c= 6.3574(6) angstrom and Z = 4. The NaKAl2O[AsO4](2) structure is built up of [Al2As2O9](2-) layers perpendicular to the c-axis which are separated by A(+) alkali layers. The [Al2As2O9](2-) layers consist of ribbons of edge-sharing AlO6 octahedra, running along the a direction and which are connected through AsO4 tetrahedra by sharing corners. The Na2KAl3[AsO4](4) structure contains [Al3As4O16](3-) layers perpendicular to the b-axis separated by A(+) alkali layers. The [Al3As4O16](3-) layer consists of a layer of corner-sharing AlO6 octahedra which are also connected to the AsO4 tetrahedra by sharing corners. (C) 2010 Elsevier Ltd. All rights reserved.