Activated Montmorillonite was applied for the sorption of pyridine as a health-toxic substance. Fourier-transform Infrared spectroscopy (FTIR), zeta potential analysis, thermogravimetric analysis (TGA), N 2 physisorption analysis and X-ray diffraction (XRD) method were used to investigate the structure and composition of Montmorillonite. The batch sorption system was used to study the effect of different parameters on the adsorption. Results had shown that neutral pH had a significant effect on the sorption of pyridine; thermodynamic calculations indicated that the adsorption of pyridine over Montmorillonite was exothermic reaction and the equilibrium capacity was slightly increased by using H 2 SO 4 as activating agent by comparison with that obtained by using HCl and H 3 PO 4. Fitting the experimental data to isotherms models indicated that the experimental data were well fitted by Fowler Guggenheim isotherm models. Finally the results obtained by FTIR and TGA proved that the relative affinity of the pyridine toward the Montmorillonite was related to the electron donor-acceptor complexes that were formed between the basic sites (nitrogen or oxygen) and hydrogens (acidic site).