In the presence of ethylenediamine template agents, a layered antimony (III) phosphonate, [NH 2 CH 2 CH 2 NH 2 ][Sb 2 {O 3 PCH(OH)CO 2 } 2 ] (1) has been synthesized by hydrothermal reaction at 140°C and characterized by single-crystal X-ray diffraction as well as by infrared spectroscopy, elemental and thermogravimetric analysis. The structure of compound 1 comprises [SbO 4 E] trigonal bipyramids (E is the lone pair electrons occupying an axial position) and [O 3 PC] tetrahedra connected by [O 3 PCH(OH)CO 2 ] 3− to form a 2D layered structure with a one-dimensional channel system, and the ethylenediamine template agent is located inside the channels.