The present work is concerned with a thermodynamic study of the three aminopyridine (AP) isomers (general formula: C5H6N2). It was achieved using three techniques: combustion calorimetry of small amounts of substance (a few milligrams), sublimation calorimetry, and differential thermal analysis. From this study, it was possible to determine the enthalpies of combustion, sublimation, and fusion of these compounds and their triple point temperatures; to discuss the relative stability of the three molecules; to determine the experimental resonance energies and compare them with the theoretical values; to determine the atomization enthalpies and compare them with the values calculated from the energetical contributions previously determined in our laboratory; to determine the enthalpy of the intermolecular bonds.Key words: aminopyridine isomers; enthalpy of combustion, of sublimation, of fusion, of inter- and intramolecular bonds.