Perovskite-type oxide La0.4Sr.6Mn0.8Ni0.2O3 showed high activity for NO decomposition and thus was taken as the catalyst for investigation. Based on the 'recycle' mechanism of NO decomposition (NO2 acts as an intermediate of O-2 formation) we reported recently, the kinetics of NO decomposition over La0.4Sr.6Mn0.8Ni0.2O3 was investigated. The NO decomposition rate was practically first-order for NO in the range 0.5-2.0 vol.% NO/He, while the reaction order varied from -0.24 to -0.08 for O-2 (0-6 vol.% O-2/He), depending on the temperature. The kinetics deduced from the 'recycle' mechanism accords well with that observed in practice by introducing the item K-6 (K-7)(1/2) P-NO (P-O2)(1/2), which reflects the reciprocity of O-2 and NO in the reaction and is introduced in the kinetics for the first time. The rates and NO2 dissociation equilibrium constants calculated from the practical reaction certified that NO2 dissociation is indeed an important step of NO decomposition, and hence suggested that the 'recycle' mechanism is believable. (c) 2005 Elsevier B.V. All rights reserved.