A simple and efficient synthetic method for preparing high-surface-area perovskites was investigated by focusing on the importance of the formation of an amorphous precursor. Hexagonal SrMnO3 with high surface area was successfully synthesized by simple calcination of the amorphous precursor prepared using aspartic acid and metal acetates instead of metal nitrates, without pH adjustment. The specific surface area reached up to ca. 50 m2 g-1, which is much larger than that for SrMnO3 synthesized by previously reported methods. The catalytic activity for heterogeneous liquid-phase aerobic oxidation was significantly improved in comparison with the polymerized complex method, and the present catalytic system was applicable to the oxidation of various substrates.