The correlation of adsorption isotherm is crucial for the successful implementation of adsorption technology. In this work, the adsorption behavior of anionic dyes, eosin Y, and indigo carmine from dilute aqueous solution on chitosan was investigated at T = 303, 313, and 323 K and P = 0.1 MPa through adsorption isotherms and thermodynamic parameters such as enthalpy change, entropy change, and Gibbs energy. The experimental data obtained in this study were used to develop a new four-parameter model for correlating liquid-phase adsorption isotherm based on the solid-liquid phase equilibrium. The new model correlates the isotherm as a function of Gibbs energy change and temperature. The overall average absolute relative deviation between the experimental and correlated results was less than 9.0%. Adsorption kinetic studies and effect of pH are reported.