Ammonium nitrate fuel oil (ANFO) samples based on fertilizer (AN-F) and ammonium nitrate porous prill (AN-PP) were studied. Tests were carried out using both a thermogravimetric analyzer and differential scanning calorimetry (TGA/DSC). Furthermore, the scanning electron microscopy analysis (SEM) of ammonium nitrate(V) (AN) concerning either their surface or cross-section was performed. Based on the SEM results, it was shown that the surface of AN-F grains was flat and slightly deformed, while the AN-PP surface was wrinkled and deformed. Furthermore, the various steps of thermogravimetric process exhibited continuous AN phase transition according to precise temperatures. From TGA analysis, a significant mass loss was found as a result of ANFO decomposition. Direct comparison of SEM and TGA/DCS data led to the conclusion that ANFO based on AN-F was characterized by lower absorption of FO in contrast to AN-PP.