The samples of NH4NO3-contg. fertilizers modified by addn. of carbonates or sulfates were heated up to 450 degrees C under He flow (60 mL/min) in thermal analyzer coupled with thermobalance and mass spectrometer. The heating rate was 5 degrees C/min. The presence of carbonate fillers in fertilizers significantly reduced the adverse effects assocd. with exothermic decompn. of NH4NO3.