We have investigated the structural changes in the added-rows of Ag-O chains at a Ag(1 10)(2 x 1)-O surface due to photo- and CO-induced elimination of O by using. scanning tunneling microscopy. The photo-induced elimination occurs only on the surface containing carbidic carbon, resulting in the structural change of the added-rows from (2 x 1) to (4 x 1) according to, the reduction of O coverage (theta(O)). The structural change due to the CO-induced elimination depends on the carbon coverage: the (2 x 1). structure is retained in spite of the decrease of theta(O) for the C-contained surface, while the structure changes sequentially from (2 x 1) to (4 x 1) and (6 x 1) for the carbon-free surface. Furthermore, the CO-induced elimination rate in the low theta(O) on the carbon-free surface is much faster than that on the C-contained surface. These results-indicate that the small amount of C atoms play an important role not only in the structural changes associated with the oxygen elimination reactions but also in the kinetics of the oxidation reaction of CO. (C) 2002 Elsevier Science B.V. All rights reserved.