The detailed study of the properties and mechanisms in the case of applied activities of coordinating compounds in various fields such as catalytic, biological, antibacterial and other activities requires the knowledge of their molecular and crystalline structure, but especially of their thermal behavior. The complexes of iron(III) with 2,6-diacetylpyridine bis((iso)nicotinoylhydrazone) were obtained by condensation reactions of 2,6-diacetylpyridine with hydrazides of nicotinic and isonicotinic acid on the matrix of iron(III) ions and by direct interaction of iron salt with the corresponding Schiff bases. In order to determine the composition, spectral characteristics, molecular and crystal structures of the complexes, elemental analysis, IR spectroscopy and single crystal X-ray diffraction were applied. The composition and structure of the studied complexes were established and can be described by the following formulas: [Fe(HL1)(NCS)2] · 0.25H2O (1), [Fe(H2L1)(H2O)2](NO3)3 · 5H2O (2), [Fe(HL2)(NCS)2] · 2.33H2O (3) and [Fe(HL2)(OH)2] · 4H2O (4), where H2L1 - 2,6-diacetylpyridine bis(isonicotinoylhydrazone) and H2L2 - 2,6-diacetylpyridine bis(nicotinoylhydrazone). The combined thermal analysis (TG-DTG-DTA) of the compounds and coordinating agents was performed in the 20-1000°C range in an air atmosphere at a heating rate of 10°C/min. Both coordinating agents, due to the similar structure, have identical heating behavior: initially the adsorbed water is eliminated, the process being completed at 80°C after the melting of the Schiff bases, at 230ºC - H2L1 and at 255ºC - H2L2. Immediately thereafter, the ligands begin to decompose, with a mass loss of 53% to 423°C, when the DTA curves for both samples show an endothermic effect attributed to the recrystallization of the intermediate compounds. The subsequent raising of the temperature leads to the oxidative degradation of the organic residue with a 100% weight loss. Complex compounds 1-4 have a different heating behavior, the decomposition process being carried out in several stages. The first stage, common to all compounds, is the elimination of the water of crystallization, which is completed at 105ºC. For all compounds, there is a major difference in the degradation of the coordinated organic ligands in relation to the initial coordinating agents, which is explained by the strong coordination bonds formed with the iron atom. Thermal degradation of compounds 1 and 3 occurs in the range of 220-510°C. A less thermal stability is registered for compounds 2 and 4 in whose internal coordination sphere water molecules and hydroxide ions are present; the decomposition process takes place in the range 180-400ºC. The residue obtained for all compounds corresponds to iron(III) oxide which remains stable up to 1000ºC.