A novel gas barrier film is developed by optimizing composition of clay materials and additives, as well as preparation process. A flexible and translucent gas barrier film can be prepared through the compact lamination of clay crystal platelets of thickness around 1 nm each. The gas permeability of the film at room temperatures to hydrogen, oxygen, nitrogen and other inorganic gases is lower than the detection limit: comparable to that of aluminum foil. Besides, the gas barrier performance of the film remains unchanged up to temperatures as high as 1000 °C.