The Ni(II), Cu(II) Co(II) and Zn(II) complexes of 2,3-hydroxyimino-4-phenyl-6-phenyazo-1-thia-4,5-diaza- cyclohexa-5-diene (H2L) were synthesized. Thermal behavior of these complexes was studied in dynamic nitrogen atmosphere by TA (thermogravimetric analysis), DTA (differential thermal analysis) and DTG (differential thermal gravimetry) techniques. the reaction order, the activation energies, the entropies, the enthalpies, the free energies, and the pre-exponential factors of the thermal decomposition reactions were calculated from the thermogravimetric curves. the kinetic analysis of the thermogravimetric data was performed by using several methods such as MacCallum-Tanner (MT), van Krevelen (vK), Madhusudanan-Krishnan-Ninan (MKN), Wanjun-Yuwen-Hen-Cunxin (WYHC), Horowitz-Metzger (HM) and Coats-Redfern method (CR) based on the single heating rate. Most appropriate methods were determined for each decomposition step according to the least-square linear regression. the Ni(II), Cu(II) Co(II) and Zn(II) complexes displayed one- or two-stage decomposition pattern when heating in a dynamic nitrogen atmosphere and metal oxides remained as end products of the complexes. the characterization of the end products of the decomposition was performed by X-ray diffraction.