Brownmillerite SrCoO2.5 (010) thin films synthesized by pulsed laser deposition became amorphous when reduced at low temperatures by CaH2, indicating that the infinite-layer structure with the square planar Co2+O4 configuration is unstable. Ferromagnetic and conducting perovskite SrCoO3 epitaxial thin films, on the other hand, were obtained topotactically at room temperature by oxidation with NaClO.