<p>N-((5-chloropyridin-2-yl)carbamothioyl)thiophene-2-carboxamide (HL) ligand which is a novel thiourea derivative and its Ni(II), Co(II) and Cu(II) complexes were synthesized. Structural characterizations of all compounds were performed with FT-IR and ¹H-NMR techniques. Moreover, the thermal behaviors of all synthesized compounds were investigated by TG/DTA techniques. Thermal stability properties and degradation reactions of all compounds were determined The HL ligand and its Co(II) complex degrade in three consecutive stages.. However, the thermal decomposition reactions of the Ni(II) complex are completed in four consecutive stages. Besides, the degradation of the Cu(II) complex is completed in five consecutive stages. X-ray powder diffraction analysis was applied to the residues remaining as a result of the thermal degradation of the complexes and the residues were determined as Co₉S₈, Ni₃S₂ and Cu_1.96S. Apparent activation energy values of each degradation stages were calculated with using Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose isoconversional methods. Graphs of change in activation energy with degradation ratio (α) were prepared and the results were interpreted.</p>