In this study, the effects of chitosan pre-treatment on the mordanting effect and dyeability were investigated in the dyeing using Japanese pagoda tree. The chitosan treatment effects were evaluated mainly focused on the colors after dyeing of cotton and nylon fabrics which were treated with acidic aqueous solution of chitosan. In the case of chitosan untreated fabrics, the mordanting effects on the cotton and nylon were insignificant and the dyeability was very low. Regardless of the mordant types(Al, Sn, and Fe), the dyed fabrics exhibited almost identical yellowish colors. In the case of chitosan treated fabrics, dark colors were obtained compared to the case of chitosan untreated and ${Delta}E$ values were increased significantly. In cotton fabrics, the most excellent result was obtained under the condition of unmordanted and chitosan treated fabrics. This verifies the fact that routin coloring matters establish direct linkages with the chitosan components, which exhibit cationic nature, easily. In nylon fabrics, the effects of mordanting treatment and chitosan treatment are so insignificant that the routin coloring matters are presumed to establish direct dyeing with the nylon molecular chains.