The kinetics and mechanism of the food dye disodium 6-hydroxy-5((2-methoxy-5-methyl-4-sulfophenyl)azo)-2-naphthalenesulfonate (FD&C Red 40) adsorption onto chitosan were studied. The effects of pH (5.7 to 7.4), chitosan dosage [(250 to 500) mg.L(-1)], deacetylation degree (42 % to 84 %), and particle size [(0.10 to 0.26) mm] were investigated. The adsorption reaction models were used to evaluate the kinetic behavior. Infrared analysis and models based on mass transfer phenomena were; used to investigate the adsorption mechanism. The maximum adsorption capacity (300 mg.g(-1)) was found at a pH 5.7, chitosan dosage of 250 mg.L(-1), deacetylation degree of 84 %, and particle size of 0.10 mm. Pseudosecond-order and Elovich models were the most appropriate to fit the experimental data of adsorption kinetics. The adsorption process was controlled by intraparticle diffusion, film diffusion, or convection according to the experimental conditions. Infrared analysis showed the chemical interaction between chitosan and food dye FD&C Red 40.