Perovskites of different La1-xSrxAl1-y-y'FeMgy'O3-delta compositions (x = 0, 0.1, 0.15, 0.2 and y = 0.1, 0.3, 0.5, 0.8) were prepared from a reactive precursor slurry of hydrated oxides. Each sample was aged between 16 and 26 h up to 1473 K. Activity in methane combustion (1%/air) was determined in a plug-flow reactor, with 1 g catalyst and 24 l/h flowrate. Gradual decrease in activity due to thermal aging was observed, the degree of activity loss being composition dependent. Nevertheless, activity of samples aged at 1370 K was nearly independent of composition. The best thermal stability showed LaAl0.65Fe0.15Mg0.2O3 perovskite. None of the magnesium substituted perovskites performed better than a La0.85Sr0.15Al0.87Fe0.13O3 reference sample. (C) 2003 Elsevier B.V. All rights reserved.