The adsorption behavior of CO on bimetallic Ni/Cu110 surfaces has been studied experimentally by thermal-desorption spectroscopy and theoretically by density-functional theory DFT calculations. The bime-tallic surfaces were produced either by evaporation of nickel or by decomposition of NiCO 4 on Cu110. Adsorption of CO at 180 K on such a bimetallic surface yields three new adsorption states with adsorption energies between that of CO on clean Cu110 and clean Ni110. The new desorption peaks from the bime-tallic surface, designated as 1 -3 , can be observed at 250, 300, and 360 K, respectively. These new states are most pronounced when 1 2 monolayer of nickel is present on the copper surface. DFT calculations, using the Vienna ab initio simulation package code, were performed to identify the most probable Ni/Cu atomic arrange-ments at the bimetallic surface to reconcile with the experimental results. It turned out that CO adsorption on nickel dimers consisting of in-surface and adjacent subsurface atoms can best explain the observed experimen-tal data. The result shows that CO adsorption is determined by local geometric effects rather than by long-range electronic effects. These findings should contribute to a better understanding of tailoring catalytic processes with the help of bimetallic catalysts.