A chitin-based biosorbent that can be used to effectively remove dyes, typical color inducers in industrial wastewater, was developed. The crosslinking agent glutaraldehyde was bonded to the hydroxyl and/or amine groups of chitin, and then polyethylenimine (PEI), a cationic polymer, was cross-linked to produce PEI-chitin. The successful preparation of PEI-chitin was confirmed using FE-SEM, BET and FTIR analysis and simple adsorption evaluation. The adsorption performance of PEI-chitin was assessed by Acid Blue 25, in terms of the pH effect, isotherm adsorption, adsorption kinetic and thermodynamic parameters. Based on the Langmuir model the maximum dye uptake at pH 2 was 177.32mg/g, and the adsorption equilibrium was attained within 120 and 500 min for two different dye concentrations (50 and 100mg/L). Desorption experiments were evaluated using 0.001-1 M NaOH, NaHCO3, and Na2CO3 as eluents. The desorption rate was highest (85.2%) when 0.01 M NaOH was employed as the eluent. It was found that the developed biosorbent could be repeatedly used three times through adsorption-desorption of Acid Blue 25.