Abstract: Adsorption of Direct Orange 39 with six sulfonic groups on chitosan fibers at different temperatures was investigated. The experimental data were analyzed and correlated with three kinds of adsorption isotherm model, namely, Langmuir, Freundlich and Redlich-Peterson. Analytical comparison of the adsorption parameters of different models and normalized deviation from the experimental showed that Freundlich isotherm exhibited more deviation from the experimental data and Redlich-Peterson isotherm fitted the best to describe the adsorption behavior of Direct Orange 39 on chitosan fibers, and adsorption is endothermic.