<p>In this work, we synthesized lanthanum cobaltite (LaCoO_{3−<i>δ</i>}) and lanthanum strontium cobaltite-based perovskites La_1−xSr_xCoO_{3−<i>δ</i>} with <i>x = </i>0.0, 0.10, 0.30 and 0.50 using the combustion method. The XRD pattern shows that the samples have a single phase without impurities. The results of refinement showed distortion decreases as Sr²⁺ content increases. Samples with <i>x = </i>0 and 0.1 are simple-phased rhombohedral perovskites, and becomes cubic for <i>x = </i>0.3 and 0.5. The oxygen deficiency increases with strontium doping and varies between 0.015 and 0.129. A strengthening of double-exchange interactions is detected via the change of Co–O distance, Co–O–Co angle and the increase in Curie temperature. The magnetic measurements indicate that a spin-glass phase occurs at low temperatures for x ≤ 0.1, which is induced by the strong compositional disorder of the Zener polaron. For x ≥ 0.3, the increased percentage of Co⁴⁺ contributes to high-temperature ferromagnetism due to long-range magnetic interactions of double exchange.</p>