The effects of ferric oxide (Fe2O3) on the pyrolysis characteristics of soybean protein and the release of precursors to nitrogen oxides (NOx) were studied using thermogravimetry and mass spectrometry. The results show that, as the content of Fe2O3 increases, there is no major difference between initial and peak temperatures of protein pyrolysis samples. Moreover, between the temperature range of 204 and 550 degrees C where weight loss mainly occurs, total weight-loss rate decreases before increasing, with obvious weight loss occurring around the temperature of 650 degrees C. Fe2O3 displays both inhibiting and promoting effects on the precipitation of nitrogen-containing gases such as ammonia (NH3), hydrogen cyanide (HCN), isocyanic acid (HNCO), and acetonitrile (CH3CN), with the inhibition effect prevailing over promotion effect on the whole.