A high-performance chemical filter for toxic gas, such as ammonia or acetaldehyde, was newly fabricated by forming a layer-by-layer self-assembly film on the surface of a fiberglass cloth. The filter was greatly superior to the conventional active carbon filter. The newly developed filter showed remarkably high performance, because it can adsorb large amounts of gas molecules by both chemical and physical adsorption. Ammonia or acetaldehyde gases react with the polyelectrolytes in the film and are adsorbed into the multilayers of the films. In this paper, we report that the performance of the chemical filter is dependent on the nano-structure of the thin polymer film coated on the fiberglass cloth.