The surface characteristics of Fe-Cu-K catalysts were determined by X-ray photoelectron spectroscopy (XPS). The surface composition of catalysts poisoned by carbonyl sulfide (COS) was investigated by XPS and compared with the composition of unpoisoned catalyst. Sputtering with Ar+ ions was used to determine the elemental distribution of poisoned catalyst by COS as a function of depth from the surface. The results showed that the sulfur content decreased at the depth increased from the catalyst surface surface, while the iron content increased along the depth increased. FeS and FeS2 were the main phases on the poisoned catalyst surface. Only alpha-Fe2O3 was found on oxide iron catalyst. Fe3O4 was the main phase of reduced catalyst treated in H-2/CO ratio of 2.1.