By introducing chitosan treatment prior to dyeing, examination was given to the effect of chitosan coated on the surface of fabrics on the color change of dyed fabric based on th e change of ${Delta}E$, a*, and b* values. At the same time, the dyeing mechanism of Caesalpinia sappan dyestuff was predicted by the investigation of the change of air-permeability ac cording to the chitosan treatment. The change of elution was investigated by the examination of the elution of metallic ions employed as mordants after soaking dyed fabrics in the solution of alkaline perspiration ba sed upon the fact that chitosan carries excellent absorption ability toward metallic ions.