The adsorption of five acid dyes onto chitosan, derived through the deacetylation of crab-shell chitin, from aqueous solutions was studied. The equilibrium isotherms were measured and analyzed with the Langmuir, Freundlich, and Redlich-Peterson equations; the results correlated well with the Langmuir equation. Kinetic studies were also performed in an agitated batch adsorber to study the effect of the initial dye concentration and the mass of chitosan. The kinetics were analyzed with the pseudo-first-order rate equation, and the rate constants were determined. The first-order kinetic model correlated the experimental concentration and time data at short times and even up to 60% of the total adsorption period in a number of systems. (C) 2004 Wiley Periodicals, Inc.