High level ab initio calculations have been performed to study the mechanism of NO decomposition by NH3+ and NH4+ in the gas phase, NH3+ + NO --> N-2 + H3O+ and NH4+ + NO --> N2H --> H3O+. The density functional theory was used to search for possible reaction pathways. The multiconfigurational second-order perturbation (CASPT2) method is applied to the most energetically favorable pathways to obtain more accurate energy diagrams. NO reacts with NH3+ and NH4+ by producing nitrogen-nitrogen bound complexes and by donating protons/hydrogens to the O atom to weaken the N-O bond and to tighten the N-N bond. Maximum activation energies for these reactions were estimated as 55.3 and 77.3 kcal/mol.