The electrical and magnetic properties of thex=0.5 composition in the perovskite system La_1–xSr_xCoO₃ , annealed in air at different temperatures, have been investigated. Results from powder XRD, ac magnetic susceptibility, high field and low field (FC and ZFC) dc magnetization, electrical resistivity and EDAX measurements revealed that differences in the properties between the samples annealed at different temperatures (1000–1300 °C) arise due to compositional inhomogeneity. A true compositionally homogeneous compound is formed when annealed in a narrow temperature region close to ca. 1150 °C. A pronounced resistivity anomaly at the Curie temperature with a maximum temperature coefficient of resistance and a well defined magnetic transition are observed for the samples annealed at 1150 °C. The results can explain most of the unusual and widely differing results reported in the literature on the electronic and magnetic properties of different compositions in the La_1–xSr_xCoO₃ system which are synthesized and processed at different temperatures.