The title complex with formally heptadentate dinucleating ligands L, [Ni2L2](py)(2)(H2O)(2) (L = C31H28N2O7 dianion), was synthesized, characterized by elemental analyses and IR spectroscopy, and structurally determined by X-ray diffraction technique. In the center-symmetric unit [Ni2L2], two phenolates and two Schiff-base imino groups of each L, as a practical tetradentate ligand, bond two Ni atoms to form square-distortionally tetrahedral coordination geometries, D-2d symmetry. This nickel(II) complex and its homologue [Cu2L2](py)(2)(H2O)(2) were both studied by TG-DTG technique under non-isothermal conditions. The relationship between weight loss and coordinations of L in each complex was inferred in the thermal decomposition processes. The most probable kinetic mechanism, Zhuralev-Lesokin-Tempelman equition, was determined by using the combined differential and integral methods, and the related values of activation energy E and pre-exponential factor A were calculated, respectively, for each complex.