The binding of chrome violet, which is a monoazo dye and involves two hydroxyl groups in the o and o’ positions to an azo group, to chitin, and partially deacetylated chitin, was examined in the presence of metal ions. Zn2+ and Cu2+ ions do not perceptively influence the binding affinity of chrome violet to chitin. In contrast, Co2+ ion enhances the binding and Ni2+ ion suppresses it. In the lower free dye concentrations the dye uptake by partially deacetylated chitin was tremendously enhanced by adding Co2+ ion in the buffer solution of pH 5. The dye uptake by the polymer was considerably increased by the addition of Cu2+ ion at pH 5 and became much larger at pH 6. The amount corresponded to that in the presence of Co2+ ion. To investigate further the action of added metal ions, a cobalt- or a chrome-complex dye was prepared, and the binding properties for the polymers were compared with those of chrome violet in the presence of Co2+ and Cu2+ ions. Some possible mechanisms for the enhancement of chrome violet binding by the addition of Co2+ and Cu2+ ions are described.