A novel coordination polymer [Mg(L)(H2O)2]·H2O] (LH2 = L-cysteic acid) has been synthesized and characterized by elemental analysis, IR and single-crystal X-ray diffraction. The crystal crystallizes in orthorhombic system, space group P212121, with a = 5.962(3), b = 11.224(6), c = 13.664(7) , V = 914.3(8) 3, Z = 4, Mr = 245.50, Dc = 1.783 g/cm3, μ = 0.445 mm–1, flack parameter = 0.32(16), F(000) = 512, the final R = 0.0458 and wR = 0.1172 for 1578 observed reflections with I > 2σ(I). The Mg(II) atom shows an octahedral geometry defined by two carboxyl O atoms from two different L-cysteic acid ligands, one carboxyl O atom and one amino N atom from the adjacent ligand, and two aqua ligands. The Mg(II) atoms are bridged by L-cysteic acid ligands, leading to a 1D infinite zigzag chain. In the structure there are extensive hydrogen bonds, through which the complex completes its 3D framework structure.