With the development of textile, increasing amounts of wastewater that contains dyes are discharged into bodies of water, thereby posing serious hazards because of the toxic and carcinogenic properties of most of these dyes. Therefore, the removal or decolorization of these dyes before their discharge into water systems is necessary. Several physical, chemical, and biological techniques have been employed to remove dyes from wastewater, among which are photochemical degradation, biological degradation, coagulation, chemical oxidation, and adsorption. Adsorption has been shown to be most promising for the removal of organic contaminants from wastewater. Chitosan (CS), a derivative desacetylated of the chitin, has attracted remarkable attention because of its non-toxicity, biocompatibility, and biodegradability. it is widely used in dye adsorption from aqueous solutions. In this work, we investigated the removal of acid dyes in aqueous solution: the red telon and the yellow irionyl by the modified chitosan: chitosan-benzylamine composite and nanoparticles of chitosan-MgO. We studied the influence of various parameters on the kinetics of biosorption as: contact time, initial concentration of the dye, the mass of biosorbent and the initial pH of the solution. The results showed that the removal of the dye depends on several factors such as pH and the contact time. The biosorption of red telon and yellow irionyl by chitosan-benzylamine composite and nanoparticles of chitosan-MgO showed better results for the removal of the dyes, the adsorbed quantities at equilibrium by chitosan-benzylamine composite and nanoparticles of chitosan-MgO are higher than those of the only chitosan.