Abstract: On the basis of rapid pyrolysis of two antibiotic mycelial wastes (AMWs), viz., penicillin mycelia waste (PMW) and terramycinmycelial waste (TMW), in a horizontal tubular quartz reactor, evolution of nitrogen functionalities and their relation to NO_x precursors were investigated with the help of XPS and chemical absorption-spectrophotometry methods.The results indicate that inorganic-N (N-IN) and amide-N/amine-N/amino-N (N-A) are two kinds of nitrogen functionalities in the raw AMWs samples, determining the predominance of NH₃-N among NO_x precursors. N-A is found to be the main one with the proportion of 81.1% and 59.0% for PMW and TMW, respectively. At low temperatures, the decomposition of N-IN and the conversion of N-A mainly occur at 150-250℃ and 250-450℃, respectively, which are two routes for most NH₃-N with yields of 20.9% (PMW) and 25.6% (TMW). While HCN-N is produced with a small amount less than 2%, having no relationship with the characteristics of nitrogen functionalities in fuels. Besides, pyridinic-N (N-6) and pyrrolic-N (N-5) are also formed and then converted with peak values at 350-400℃. At high temperatures, the conversion of N-6 and N-5 is prevailing, leading to the basically equal increments on NH₃-N and HCN-N. Simultaneously, a minor amount of more stable quaternary nitrogen (N-Q) and N-oxide (N-X) is produced. Typically, due to the rapid decomposition of N-IN and labile N-A at low-temperature pyrolysis, nitrogen removal can reach up to 40% while energy loss can be controlled within 25% when pyrolyzing at 250-300℃. As a result, low-temperature pyrolysis could be an effective method for nitrogen removal whereas preserving the energy in AMWs.