Two new ternary vanadyl(IV) orthophosphates, RbVOPO4 and CsVOPO4, have been prepared and their structures have been determined from single-crystal X-ray diffraction data. They crystallize in the orthorhombic space group P212121 with a = 7.8669(9), b = 7.5848(8), c = 8.3771(10) Å, V = 499.8(1) Å3, Z = 4, and R = 0.029 for RbVOPO4, and a = 7.3665(15), b = 7.6146(15), c = 9.8035(17) Å, V = 549.9(2) Å3, Z = 4, and R = 0.029 for CsVOPO4. These two compounds consist of intersecting tunnels running along each axis, and the alkali metal cations are located at the intersection of these tunnels. Unlike other AM OPO4 structures (A = alkali metals; M = Ti, V), the frameworks of the title compounds are built up from discrete VO5 pyramids and PO4 tetrahedra. Each VO5 pyramid shares its four basal oxygen atom vertices with three different PO4 tetrahedra. One of the phosphate groups is coordinated to the V atom as a bidentale ligand. These two closely related structures are not isomorphous, differing in the orientation of vanadyl oxygens.