The objective of this study is to investigate the efficacy of chitosan treatment to improve dye uptake of bamboo colorants on cotton and ramie. The surface of fiber was modified by chitosan treatment to form dye sites. And the effect of chitosan treatment on dyeability was investigated in terms of color strength, shade, and fastness. The antimicrobial activity of the dyed sample was also evaluated. With increasing chitosan concentration dye uptake (K/S) increased sharply up to 0.15~0.25% and slowly thereafter. Dye uptake was increased sharply to 30 min of dyeing time, resulting shorter dyeing time compared to dye the untreated sample. Ramie showed higher improvement of dye uptake than cotton. The color of dyed ramie fabrics changed to duller, darker and more yellow greenish, in general, with the increase of chitosan treatment concentration. Colorfastness of the dyed fabrics was fair irrespective of chitosan treatment, except washing fastness of the chitosan treated cotton. The dyed fabrics were shown 99% of bacteria reduction rate against both of Staphylococcus aureus and Klebsiella pneumonia.