Two two-dimensional and three-dimensional coordination-polymer, [Ni(2,2′,5,5′-bpdc) (H2O)]•H2O (1) and[Ni(2,2′,6,6′-bpdc)2]•4H2O (2) were obtained via hydrothermal reaction between NiCl2•6H2O and 2,2′-bipyridine-5,5′-dicarboxylic acid (2,2′,5,5′-bpdc), 2,2′-bipyridine-6,6′-dicarboxylic acid (2,2′,6,6′-bpdc) respectively, and were characterized by infrared spectra, thermogravimetric analysis and single crystal X-ray diffraction. The 2,2′,5,5′-bpdc and 2,2′,6,6′-bpdc ligands in compound 1 and 2 show different coordination modes respectively. The 2,2′,5,5′-bpdc ligand acts as pentadentate connector to coordinate with three different Ni(II) ions, and further extend to form square grid framework of compound 1; while 2,2′,6,6′-bpdc acts as tridentate ligand to chelate one Ni(II) ion to construct discrete monomeric unit, and those discrete units of [Ni(2,2′6,6′-bpdc)2]•4H2O are joined into 3-D framework via rich hydrogen bonding interactions. Thermogravimetric analysis revealed that both complex (1) and (2) display considerable thermal stability. CCDC 773845 & 773846.