The thermal decomposition of tetrahedral cobalt(II) complexes with 3(5)-amino-4-acetyl5(3)-methylpyrazole (HL) of the general formula [Co(HL)2X2] (X=Cl, Br, I, NCO, NCS) and octahedral [Co(HL)2(H2O)4](NO3)2 and [Co(HL)2−N(CN)2}2] complexes was investigated in air atmosphere in the interval from room temperature to 1000°C. Decomposition of the complexes occurred in several successive endothermic and exothermic processes, and the residue was in all cases CoO.