We report the solid-phase self-assembly of nanostructures from amorphous thin film of aromatic peptides. The thickness of amorphous peptide film could be precisely controlled down to similar to 50 nm. Aligned nanostructures were grown from the film either by changing water activity in the vapor phase or by applying high thermal energy. The growth of peptide nanorods on solid substrate occurred via a water-vapor-mediated self-assembly process. We found that the peptide nanostructures could be "reversibly" dissociated and reassembled depending on the chemical composition of the vapor phase. We also observed that the phase transition of aromatic peptide occurs at extremely high temperatures above 100 degrees C, and the thermal aging of amorphous film resulted in the formation of peptide nanorods. In this work, the formation of peptide nanostructures from amorphous thin film was investigated by multiple analytical tools such as electron and atomic force microscopies, vibrational and diffraction spectroscopies, and differential scanning calorimetry. To the best of our knowledge, this is the first report for the self-assembly of peptides into nanostructures starting from amorphous thin film.