Selective oxidation of hydrogen sulfide (H2S) was studied on zeolite-NaX and zeolite-KX. Elemental sulfur yield over zeolite-NaX was achieved about 90% at 225 oC for the first 4 hours, but it gradually decreased to 55% at 40 hours after the reaction started. However, yield of elemental sulfur on zeolite-KX was obtained within the range of 86% at 250 oC after 40 hours. The deactivation of the zeolite-NaX and -KX catalysts was caused by the coverage of a sulfur compound, produced by the selective oxidation of H2S over the catalysts. The coverage of a sulfur compound over the zeolite-NaX and -KX was confirmed by the TPD (temperature-programmed desorption) tests utilizing thermogravimetric analysis and FT-IR analysis. Even though high temperature was required to prevent the deactivation of zeolite-NaX, the temperature cannot be raised to 250 oC or above due to the SO2 production and the decrease of thermodynamic equilibrium constant. Zeolite-KX was superior to the zeolite-NaX for both its selectivity to elemental sulfur and its resistance to deactivation in the selective oxidation of H2S.