The release behavior tests of NOx precursors from wheat straw during pyrolysis in argon and gasification in 5% O-2/95% Ar and 5% CO2/95% Ar were performed using a thermogravimetric analyzer (TGA) coupled with a Fourier transform infrared (FTIR) spectrometer. The results show that heating rate and particle size have substantial effects on the selectivity of N-conversion due to the selectivity of cracking of cyclic amides and the secondary reaction influencing the formation of NH3, HCN and HNCO. The atmosphere influences the N-selectivity to HCN, NH3, NO and HNCO. The formation of HCN and NH3 in 5% O-2/95% Ar is a result of competition among the opposing effects of O-2. The presence of O-2 promotes the yields of HCN and HNCO evidently, and HNCO seems to be a favourable product from biomass-N compared in Ar atmosphere although HCN yield is a little bigger than that of HNCO. The use of CO2 reduces the formation of HCN, the yield of NH3 keeps essentially constant compared in Ar, and the emission of HNCO is suppressed. NH3 seems to be a favourable product from biomass-N in 5% CO2/95%Ar. (C) 2009 Elsevier Ltd. All rights reserved.