Molecular self-assembly is a technology in which different structural components spontaneously form assemblies with special functions through weak, reversible non-covalent interactions on the basis of molecular recognition. The amphiphilic and biocompatibility of polypeptides make it has natural advantage in self-assembly at the air-water interface. In this work, the self-assembled films of palmitoyl pentapeptide-4 (PP4) and dye molecules were prepared by Langmuir-Blodgett (LB) technology. It was found that the PP4/dye composite film had good acid-alkali gas response. In addition, the LB film prepared by PP4 and methyl orange (MO) showed chiral signal, which was reflected in the circular dichroism spectrum. The current research work provides new clues for the preparation of functional self-assembled films and their applications as gas sensors and chemical switches.