Two new isostructural mixed-valent tellurium oxides, A(4)[Te56+Te34+]O-23 [A = Rb (1) and K (2)], have been synthesized by solid-state reactions and characterized by X-ray diffraction and infrared spectroscopy. Compound 1 could be prepared by hydrothermal reaction as well. These compounds, as determined from the single-crystal X-ray structure of 1, consist of corrugated [Te6O23] layers, built from corner-connected TeO6 octahedra and TeO5 square pyramids. These layers are connected to one another by tetravalent telluriums, having square-pyramidal and disphenoid geometries. Both compounds crystallize in the orthorhombic space group Pna2(1) (33) with Z = 4 and have the following unit cell parameters: For 1, a = 19.793(4), b = 14.664(4), and c = 7.292(4) A. For 2, a = 19.573(3), b = 14.448(2), and c = 7.273(8) angstrom.