. We demonstrate that banana-shaped molecules 1,3-phenylene bis(4-methoxybenzylidene amine) can assemble themselves into diffraction gratings when the melt of the banana-shaped compound, which was sandwiched between two pieces of glass substrates, is cooled to room temperature. Polarizing optical microscopic characterization shows that a pattern of periodic modulation of the refractive index can be developed in the thin films formed by the banana-shaped compound. Despite the gratings are groove free, their optical properties are the same as classically ruled gratings. Our work provides an alternative method for manufacturing diffraction gratings by harnessing the self-assembly of banana-shaped molecules.