The N 2 H+O potential energy profile was studied at the CCSD(T)/6-311G++(df,p)//MP2/6-311G(d,p) level. Reactions associated with four intermediates(cis-HNNO, trans-HNNO, NNHO, and NNOH) were investigated. The results indicate that N 2 H+O reaction toward H+N 2 O is more favored than that toward N 2 +OH, consistent with previous experimental studies. The pathways for the two reactions are found to go through cis-HNNO, transition state, and finally to the products. The N 2 H+O→NH+NO reaction was studied in detail. Product NO in such a reaction is likely to occur via cis-HNNO, followed by trans-HNNO, and finally dissociates into NH+NO. These results suggest that N 2 H+O→NH+NO is an important channel in NO production.