The mixed-metal complex of copper(II) and magnesium(II) ions with glutamate has been firstly synthesized by self-assembling, and characterized by elemental analyses, IR spectra and electronic spectra. The structure of the complex has been determined by single-crystal X-ray diffraction. The [CuMg( l-glu) 2 (H 2O) 3]·2H 2O ( l-glu = l-glutamate) complex has a one-dimensional polymeric structure, in which Cu II and Mg II ions are bridged by glutamate. Each Cu atom exhibits distorted square pyramidal five-coordination, with two glutamate ions acting as a bidentate ligand through the amino N and the α-carboxylate O atoms in trans positions in the equatorial plane, forming two glycine-like rings, and with a water molecule in apical position. Each Mg atom is coordinated in a slightly distorted octahedral geometry by two γ-carboxylate O atoms from two glutamate ions and by four water molecules. The average CuO, CuN and MgO distances are 2.048(2), 1.979(3) and 2.084(2) Å, respectively. The coordination patterns of glutamate ion in different glutamate Cu II complexes are also discussed.