A new open-framework germanium oxide Ge10O21(OH)(N4C6H21)-N-. has been hydrothermally synthesized at 180 degreesC for 6 days by using the tris(2-aminoethyl)amine (tren) molecule as a structure-directing agent. This compound was characterized by means of single-crystal X-ray diffraction and FTIR. It crystallizes in the noncentric monoclinic system Cm (a = 14.0495(2) Angstrom, b = 12.8058(3) Angstrom, c = 9.2637(2) Angstrom , beta = 128.406(1)degrees, Z = 4). Its three-dimensional framework is built up from GeO4 and GeO3(OH) tetrahedra connected by vertexes to GeO5 trigonal bipyramids and GeO6 octahedra. A pseudo-cubic building unit (''4-3'' subunit) consists of four GeO4 tetrahedra, two GeO5 trigonal bipyramids, and one GeO6 octahedron (Ge-7). In the ''4-3'' block, the GeO5 trigonal bipyramids share a common edge, This Ge-7 entity is linked to three tetrahedral units GeO3X (X = O, OH), and this forms an original decameric building unit Ge10O21(OH) which is new in the germanates crystal chemistry. It results in a relatively dense open framework composed of pear-shape cavities (7(8)6(2)5(2)4(4)3(2)) encapsulating the triprotonated tren molecule. The inorganic network contains small pores delimited by 7-ring channels running along [001].