The adsorption of a CH3SH molecule on acid zeolite has been investigated by theoretical ab initio and density functional theory DFT methods. The zeolite was modeled by a cluster of 10 membered rings whose formula is (SiH2)(9)(O)(9)Al](OH)(2) containing 43 atoms and only one Bronsted acid site (T10-OH). The calculations were performed at Hartree-Fock and the BLYP/DFT levels of theory with the 6-31+G(d,p) basis set and taking the C-s symmetry restriction for the isolated species and the adsorption complex geometry. After interaction of CH3SH with the zeolite cluster, a van der Waals 1:1 adsorption complex CH3SH-T10-OH is formed, with a geometry that is dominated by the formation of a hydrogen bond between the S atom of CH3SH and the H atom of the hydroxyl group S- -H of the T10-OH moiety. Similar calculations were carried out for the adsorption of methanol CH3OH with the T10-OH cluster for comparison. For both complexes the structural, energetic, vibrational, and topologic properties were analyzed. Additionally, the deprotonation energy for the T10-OH cluster was determined and our BLYP value of 1374 kj/mol is comparable to previous experimental and theoretical determinations from the literature. The structural results indicate that the complex is linear and the interaction energies indicate that the adsorption of the sulfur compound is much less than the oxygenated alcohol, which may be accounted for by the differences in the electronegativities of S and 0 atoms. A comparison of the calculated interaction energy for the CH3SH-T10-OH complex indicates that the nature of CH3SH adsorption is similar to other sulfur-zeolite complexes from the literature. The frequency shifts of the OH vibrational mode of the zeolite are found to be negative on complex formation and resemble the corresponding shifts of the experimental adsorption of CH3SH in SiO2 and H-ZSM5 zeolites. Finally, the analysis of the topologic properties of the complexes and the isolated molecules indicate that additional chemical interactions occur between the O atoms of the zeolite network and the H atoms of the CH3SH and CH3OH molecules, which increases the stability of the complexes.