Complex reaction mechanism of HCNO + OH were investigated at the CCSD(T)/6-311++G(3df,2p)//B3LYP/6-311++G(3df, 2p) level. The results show that this reaction has four main entrance channels. From initial adducts sixteen different pathways lead to products. The most favorable channel involves the barrierless entrance isomer (HC(OH)CNO) which is formed by OH adding to C atom. Products of (CO + NHOH) and (CHO + HNO) are the most favorable, (H2O + NO), (H-2 + OCNO), (H-2 + CO + NO), (CO + NH2O) are minor pathways. Heats of reaction are predicted at the CCSD(T)/CBS level. Our results are in good agreement with available experiment. (C) 2014 Elsevier B. V. All rights reserved.