Thermal decomposition taking place in solid state complex, NiC2O4-2H(2)O, has been investigated in air by means of TG-DTG/DTA, DSC, XRD. TG-DTG/DTA curves showed that the decomposition proceeds through two well-defined steps with DTA peaks closely corresponding to the weight loss obtained. XRD showed that the final decomposition product of NiC2O4-2H(2)O was NiO. Kinetics analysis of NiC2O4-2H(2)O decomposition steps was performed under non-isothermal conditions. The activation energies were calculated through Friedman and Flynn-Wall-Ozawa (FWO) methods, and the most possible kinetic model function has been estimated through the multiple-linear regression method. The activation energies for the two decomposition steps of NiC2O4. 2H(2)O were 171.1 +/- 4.2 and 174.4 +/- 8.1 kJ/mol, respectively. (c) 2005 Elsevier B.V. All rights reserved.