The aim of this study is to prepare and characterize chitosan (CS) and cross-linked chitosan (CCS) by glutaraldehyde in order to obtain better natural adsorbents to remove fluoride ions from aqueous solutions. The characterization was carried out by Fourier-transform infrared spectrometry (FTIR) and X-ray diffraction (XRD).These adsorbents were used to remove the fluoride ions in aqueous solution in a batch reactor. Experiments have been carried out to study the influence of certain parameters such as initial fluoride concentration, adsorbent dose, pH solution and contact time on adsorption capacity in order to determine the optimum values leading to better adsorption. The results obtained showed that the adsorption kinetics of the fluoride ions on the two adsorbents is described by the pseudo-second order model and that the adsorption isotherms are described by the Langmuir mathematical model.