This research article published by Biointerface Research in Applied Chemistry, Volume 8, Issue 3, 2018Interaction of chitosan with fluoride (F- ) has been studied using experimental and computational methods. Chitosan was extracted from prawns shells and modified by cross-linking with glutaraldehyde and protonation using concentrated hydrochloric acid. Modified and pristine chitosan were characterized using XRD, FT-IR and UV–Vis. Adsorption of Ffrom solution was determined using ion selective electrode meter. β-D-glucosamine (β-GlcN) monomer was used to model chitosan. Optimization of molecular geometry, harmonic vibrations analysis and interaction energies with fluoride were computed using DFT with B3LYP/ 6-311**G (d,p) level of theory. Electronic absorption spectra of β-GlcN was calculated by Time Dependent–DFT using the same level of theory and compared with UVVIS spectra of pristine chitosan. Firefly 8.1.1 program package was used for all computations. Computed IR frequencies were assigned using Chemcraft visualization software and compared with experimental FT-IR spectra of chitosan and literature values. Equilibrium geometry calculated was compared with X-ray diffraction. Results indicated that computed parameters matched well with experimental results and confirmed that electropositivity hydrogen atoms of amine and its adjacent hydroxyl groups in chitosan influenced the adsorption of fluoride from solution by electrostatic attraction also, that protonation of the amine group increased adsorption capacity significantly.