Sulfur tolerances of alpha-Al2O3 supported noble metal (Rh, Pt, Ir, and Ru) catalysts for steam methane reforming (SMR) at 700 degrees C were examined. Methane conversions over all catalysts decreased in the presence of dimethyl sulfide (DMS) as a sulfur contaminant in the SMR feed. Higher DMS concentration in the SMR feed accelerated the degradation rate of all catalysts. In general, sulfur poisoning is one of major reasons for catalyst degradation. The catalysts showed different degradation behaviors depending on the DMS concentration and the active metal species. Rh and Ru catalysts were deactivated completely within the first few hours of SMR with DMS. Methane conversions over Pt and Ir catalysts also decreased to some extent within hours, but subsequently remained unchanged. Pt and Ir catalysts poisoned by sulfur were fully regenerated after stopping the DMS feed, and Rh catalyst poisoned by sulfur recovered to some extent, whereas Ru catalyst poisoned by sulfur was little regenerated.