In this paper a wide range of La1-xSrxMnO3 (x = 0-0.7) perovskites was synthesized by Pechini route, characterized by XRD (including high temperature measurements), XPS, differential dissolution phase analysis, TPR H-2, oxygen exchange and tested in N2O decomposition at 900 degrees C. At low degree of Sr substitution for La (x <= 0.3), high catalytic activity was found for perovskites with hexagonal structure (x = 0.1-0.2) and can be related to fast oxygen mobility caused by the lattice disordering during polymorphic phase transition from the hexagonal to cubic structure. For multiphase samples (x > 0.3) increase of activity and oxygen mobility can be attributed to the formation of the layerstructured perovskite-LaSrMnO4 on the surface.