In this work, the group contribution method of Chickos et al. was applied to estimate the fusion enthalpy of isonicotinic acid, and the obtained result (29.2 kJ.mol(-1)) showed a large difference with the value (135 kJ.mol(-1)) as reported from literatures and as determined by differential scanning calorimetry (DSC). The results of DSC/TG measurement showed that the phase transition of isonicotinic acid from 187.27 degrees C to 277.47 degrees C underwent a sublimation process, with a sublimation enthalpy of 128.03 kJ.mol(-1). An efficient analytical technique combining pyrolysis and gas chromatography/mass spectrometry (Py-GC/MS) was used to prove this conclusion. (C) 2016 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.