The current work is focused on the study of the bio-sorption of hexavalent chromium from aqueous solution using sisal natural fiber (Agave sisalana) treated by various chelating agents (ligands) such as urea (UR), thiocarbamide (TC), ethylenediaminetetraacetic acid (EDTA), and diphenyl carbazide (DCZ). The fiber treatments were investigated using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning electron microscope (SEM). The kinetics of chromium bio-sorption was studied in batch presses under the effect of some physicochemical factors such as the nature of chelating agent (F@UR, F@TC, F@DCZ, and F@EDTA), adsorbent dose (2-10 g. L-1), chromium initial concentration (100-500 mg.L-1), solution pH (1-6), and batch temperature (20 degrees C-50 degrees C). This study resulted in an optimum adsorption at a chromium initial concentration of 100 mg.L-1, at pH 2, and at 20 degrees C. The obtained results showed clearly that the treatment with chelating agent boosts the adsorptive capacity of A. sisalana fibers Cr(VI) 10.9 mg.g(-1) to 58.6 mg.g(-1). The modeling study showed that the adsorption kinetics obey the pseudo-second-order model, with an R-2 in the range of 0.991 and 0.999. The bio-sorption isotherms followed the Langmuir model; the maximum uptake capacity of (F@N, F@UR, F@TC, F@DCZ, and F@EDTA) was found to be respectively, 12.3 mg.g(-1), 25.33 mg.g(-1), 28.73 mg.g(-1), 42.54 mg.g(-1), and 61.45 mg.g(-1). The determined adsorption thermodynamics parameters such as enthalpy, free energy, and entropy showed that the adsorption process is exothermic, spontaneous, and has a stable configuration. (C) 2017 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.