The purpose of this study is to investigate the feasibility of applying the chitosan for a natural mordant. The chitosan, a natural chelate macromolecule, is acquired from the crustacean. Investigation was focused on the change of the dyeability according to the chitosan treatment based on the Caesalpinia sappan and the color change of the dyed fabric according to the application of heavy metal mordant. The change of air permeability of the fabric with the dyeing condition was also investigated systematically. The effect of dyeing with/without mordant on the air permeability of the fabric after the chitosan treatment. It seems that the increase in the dye-uptake is attributable to the fact that chitosan forms a complex with the Caesalpinia sappan and Al during mordant dyeing of cotton fabric. For nylon fabric, the darkest color was achieved on the occasion of non-mordant dyeing of the fabric. The mordant treatment or chitosan treatment, however, reduced the dyeability. While the dyed nylon fabric could maintain the same air permeability as the grey nylon fabric, the cotton fabric lowered the air permeability after dyeing.