Following the theoretical work on the isomerization reactions of the formaldiminoxy (CH2NO) radical, this paper reports the results of the ab initio quantum chemical study of the decomposition reactions of the various isomers, using the Gaussian-2 (G2), CASSCF, CASPT2, and QCISD(T) methods and basis sets that range from cc-pVDZ and cc-pVTZ to the 6-311 + G(3df,2p) of G2. A total of 24 dissociation reactions of 11 isomers and their rotamers have been investigated. The lowest energy reactions occur for molecules with a NCO-chain backbone, which yield HCN, HNC, OH, NH2, CO, HNCO, and H as primary products. The reaction that could compete with the above is the CH bond fission in CH2NO, giving H + HCNO as products.