The modification of acidic properties resulting from H2S adsorption on the NaY zeolite were studied by IR spectroscopy using pyridine and 2,6-dimethylpyridine as probe molecules. A very small fraction of H2S adsorbs dissociatively on NaY whereas the main part of H2S interacts nondissociatively, either by coordination with Na+ cations or by H-bonding. Evacuation at room temperature (RT) eliminates all the molecular H2S species. Both probe molecules detected Bronsted acidity in the presence of H2S but this acidity is almost completely eliminated by pumping at RT. No link between the variation in the number of protonated species and the variation in the intensity of the OH bands appears. On the contrary, there is a relationship between the presence of molecular H2S and the detection of protonated species. These results show that coordination of H2S on cationic sites leads to a modification of the electronic repartition in the hydrogen disulfide molecule, giving rise to the appearance of a positive charge on the hydrogen atom of the molecular H2S, which, thus, presents a proton-donating ability.