Abstract: The release of NO_x precursors (NH₃, HCN and HNCO) in the pyrolysis of two nitrogen-rich biomass materials, viz., soybean straw (SBS) and fiberboard (FB), were investigated by thermogravimetric-Fourier transform infrared spectroscopy (TG-FTIR, for slow pyrolysis) and horizontal tubular reactor-X-ray photoelectron spectroscopy (HTR-XPS, for rapid pyrolysis); the effects of final temperature, heating rate and nitrogen form in biomass on the release characteristic were considered. The results indicate that the evolution pathway is related to the form of nitrogen in biomass; nitrogen in SBS (SBS-N) is mainly converted to NH₃ during the secondary cracking reaction, whereas nitrogen in FB (FB-N) is transformed to NH₃, HCN (rapid) and HNCO (slow) during the primary pyrolysis reaction. Nitrogen in biomass (fuel-N) is inclined to convert to nitrogen in char (char-N) at low temperature and to nitrogen in tar (tar-N) or NO_x precursors at high temperature (>600℃), which suggests that a pyrolysis temperature below 600℃ can suppress the release of NO_x precursors. SBS-N and FB-N are characterized by protein and amide, respectively, which are partly converted to pyrrolic-N and pyridinic-N in char, forming preferably NH₃ and HCN, respectively.