A new 4-chlorobenzoic acid bridge Co(II) complex [Co-2(2,2'-bpy)(2)(mu-L)(2)(L)(2)(mu-H2O)] (HL = 4-chlorobenzoic acid) has been obtained by hydrothermal synthesis, and X-ray single-crystal diffraction analysis shows that it crystallizes in the monoclinic system, space group C2/c with a = 22.537(5), b = 16.212(3), c = 15.306(3) angstrom, beta = 124.37(3)degrees, V = 4616.1(16) angstrom(3), M-r = 1070.45, D-c = 1.540 g/cm(3), Z = 4, mu = 1.012 mm(-1), F(000) = 2176, the final R = 0.0338 and wR = 0.0810. The title complex is composed of dinuclear [Co-2(2,2'-bpy)(2)(mu-L)(2)(L)(2)(mu-H2O)] molecules. Each Co(II) atom is coordinated by two nitrogen atoms from one 2,2'-bipyridine ligand, three oxygen atoms from three 4-chlorobenzoic ions and another oxygen atom from one water molecule. The two Co(II) atoms are connected by two 4-chlorobenzoic ions and one bridged water molecule. The dinuclear molecules are interlinked by hydrogen bond and pi-pi stacking interactions into a three-dimensional supramolecular network.