Catalytic direct decomposition of t-butanethiol (TBT) into hydrogen sulfide over zeolites without hydrogen addition was examined as a new desulfurization process for fuel cell systems. TBT is a widely used odorant in pipeline natural gas, and was easily decomposed into hydrogen sulfide and isobutene over H-Y and H-beta at low temperatures of 25-150 . However, catalyst deactivation of H-beta was observed at 60 and oligomerized products of isobutene were observed on the catalyst surface after long reaction times. The deactivation rate of TBT decomposition over H-beta increased with higher acid amounts of H-beta. The amount of oligomerized products deposited on the catalyst increased with lower TBT conversion in the initial stage of reaction. The deposition of oligomerized products and catalyst deactivation decreased after several hours. The amount of the oligomerized products deposited on the catalyst reached approximately 6 wt% after 8 h and remained constant after 125 h over H-beta (Si/Al 92.5) at 150 . The initial TBT conversion was constant during 125 h.