The effect of high purity chitosan was studied on its application to the natural dyeing using Rhusjara ica. In the dyeing experiment, examinations were introduced on the difference between the chitosan treated fabrics and chitosan untreated fabrics, and on the difference according to the type of mordanting agents and the mordanting methods. Dyeing was carried out for the chitosan treated and untreated fabrics under the conditions of non-mordanting and Al, Sn, Fe mordanting. As a result, we found that, in the case of cotton, chitosan untreated fabrics were not dyed enough, and the dyeing effect was not developed even though the mordanting was introduced. However, the chitosan treated fabrics developed excellent dyeing result even in the non-mordanting case. Through the results of cotton fabric dyeing, it was presumed that the dyeing affinity of the chitosan toward the Rhusjara ica, which prefer specific dyestuff (mainly black color), is selectively high. In the case of nylon, the dyeing effect is not developed easily under all conditions regardless of the chitosan treatment or the mordant treatment. It was inferred that a certain portion of the Rhusjara ica dyestuff made direct bonding with the functional elements in the nylon molecules without the help of the mordant. Through the results of nylon fabrics, it was presumed that some functional elements of the nylon molecules had selective affinity toward the specific colorant (mainly yellow color) of the Rhusjara ica.