A novel 3D cadmium carboxyphosphonate containing left-hand helical chains, Cd 3 Cl 2 [(O 3 PCH 2 –N(H)C 5 H 9 –COO) 2 (H 2 O) 2 ]·4H 2 O 1 has been synthesized by hydrothermal reaction at 120°C and structurally characterized by single-crystal X-ray diffraction as well as with infrared spectroscopy, elemental analysis and thermogravimetric analysis. In compound 1, the hexanuclear clusters based on Cd(1)O 4 Cl 2 , Cd(2)O 4 Cl 2 , Cd(3)O 6 and CPO 3 polyhedra are interconnected through carboxyphosphonate ligands to form a 3D open-framework structure with channel system. The result of connections in this manner is the formation of 20- and 30-atom rings that are parallel to one another and run in the a-axis direction. It is interesting that a type of left-hand helical chain is formed by HL 2− ligands bridging Cd 3 ions running along the b-axis.