In this study, 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 bound to the hydroxyl and/or amine groups of chitin, and then polyethylenimine (PEI), a cationic polymer, was crosslinked to produce PEI-chitin. In order to elucidate the optimal conditions for the preparation of chitin-based adsorbents, various factors were evaluated such as the degree of chitin deacetylation, crosslinking agent concentration, PEI concentration, and chitin particle size. The optimal preparation conditions of PEI-chitin were judged by its adsorption capacity for Reactive Yellow 2. The successful preparation of PEI-chitin was confirmed using FE-SEM and FTIR analysis and simple adsorption evaluation. The adsorption performance of PEI-chitin was assessed by Reactive Orange 16 (RO16), Acid Blue 25 (AB25), and Acid Red 18 (AR18) in terms of the pH effect, isotherm adsorption, adsorption kinetic and thermodynamic parameters. The results show that the maximum adsorption amount calculated using the Langmuir model was 266.3 mg/g (RO16), 177.32 mg/g (AB25), and 141.9 mg/g (AR18), respectively at a pH 2, and the adsorption equilibrium was attained within 60 min (RO16), 500 min (AB25), and 240 min (AR18) for initial dye concentrations of 100 mg/L, respectively. Desorption experiments were carried out using ammonia/ethanol mixed solution (2:3, v/v), 0.001 ~ 1 M NaOH, NaHCO3, and Na2CO3 as eluents. The desorption rate was highest when ammonia/ethanol mixed solution was used to eluent for RO16, and when 0.01 M NaOH was employed as the eluent for AB25 and AR18. We confirmed that the PEI-chitin could be repeatedly used at least three times through reusability studies.