Lanthanum manganite (LaMnO3) with magnesium (Mg) substituted the A- and B-sites were reported for the first time in this work. The Mg substituted LaMnO3 catalysts were prepared by means of citric acid sol-gel method. The impact of partial substitution of Mg and its substitution site on the catalytic performance of LaMnO3 in nitric oxide (NO) oxidation was investigated. Through series of characterizations, it was found that Mg substitution at both A- and B-sites improves the specific surface area, Mn4+ content, reactivity of surface oxygen species, redox property and NO adsorption capacity of LaMnO3. However, Mg substitution at the A-site of LaMnO3 can cause the total charge imbalance of B-site, which significantly improves the amount and reactivity of surface active oxygen species. Therefore, the catalytic activity of the samples decreases in the order: La0.9Mg0.1MnO3 > LaMn0.9Mg0.103 > LaMnO3. This study will shed more light on the fundamental understanding and designing of perovskite catalyst. (C) 2020 Elsevier Inc. All rights reserved.