The complex metal oxides xLa-Sr-Co-Fe/MgO (x = 10-80 wt %) were prepared via a one-pot method for NO direct decomposition. The X-ray diffraction results show a gradual transformation of La-Sr-Co-Fe oxide from the Ruddlesden-Popper structure (A2BO4) to the perovskite structure (ABO3) with increasing x accompanied with Mg doping into the lattice of La-Sr-Co-Fe oxide. The NO direct decomposition activity decreases with x when x ≤ 60% and then increases with further loading. The 10% La-Sr-Co-Fe/MgO sample shows high activity and high oxygen resistance with a NO conversion to N2 of ∼46% in the presence of 10% O2 at 850 °C (W/F = 1.5 g s/cm3). Several characterization techniques have been employed to reveal the composition-structure-activity relationship. The MgO component increases the sintering resistance of catalysts, and thus, the surface area increases with the MgO content. The reducibility of Co/Fe species, content of oxide ion vacancies at the surface, mobility of lattice oxygen, and content of NO sorption decrease with x for x ≤ 60% and then increase with a further increase in x, which are responsible for the activity variation.