We report a synthesis pathway in molten salts toward ligand-free nanoparticles of the layered perovskite La0.5Sr1.5MnO4 (l-LSMO) and of the pseudocubic perovskite La0.7Sr0.3MnO3 (pc-LSMO). These particles are readily implemented as oxygen reduction reaction (ORR) electrocatalysts in alkaline conditions. They show high ORR selectivity for the 4-electron reduction of O2 in water. Among these two materials, pc-LSMO nanocrystals of 20 nm diameter exhibit high mass-normalized ORR activity for a perovskite material (21.4 A g–1oxide at 0.8 V/RHE) thanks to their relatively large surface area, high crystallinity, and electron mobility. These features provide pc-LSMO nanocrystals with remarkable stability compared to state-of-the-art perovskites, for instance, only a 5% increase of the overpotential at −0.05 mA cm–2oxide over 40 h. Thus, pc-LSMO nanocrystals are the most stable perovskite ORR electrocatalyst reported to date. This performance combined with high activity, high selectivity, and the absence of precious metals make La0.7Sr0.3MnO3 nanocrystals one of the best compromises for alkaline oxygen reduction reaction.