The adsorption of reactive dyes onto chitin (deacetylation degree = 5%) was investigated from aqueous solutions at pH 3. Ten reactive dyes were examined, including 5 dyes from the helactine group, 3 dyes from the polactine group and 2 dyes from the remazol group. The K and b constants were calculated from the Langmuir equation that assumes the presence of two sites of different nature. It was found that the dye adsorption on chitin in type I and II sites differed in both the adsorption affinity and maximum adsorption capacity. Based on the dimensionless separation factor RL it was found that the dye adsorption mechanism in type I sites was an ion exchange, whereas in the case of type II sites it was a physical adsorption. A correlation was found between dye adsorption on chitin and the number of sulfone groups in a dye molecule. However, neither molecular weight nor the number of aromatic rings was correlated with dye adsorption.