A detailed quantum chemical study is performed on the mechanism of the NCO + HCNO reaction, which has never been studied by theory. The potential energy surface for this reaction is characterized at the B3LYP/6-31 1++G(d,p) level of theory, combined with high-level CBS-QB3 single point energy calculation. Four possible product channels have been investigated. From the calculations it can be seen that the formation of HCN + NO + CO is the dominant product channel, while the pathway to products of HCNN + CO2 is expected to be minor one, and these conclusions are in good agreement with the experimental results. (C) 2007 Elsevier B.V. All rights reserved.