Infrared reflection absorption spectroscopic (IRRAS) measurements were conducted for carbon monoxide (CO) adsorption on Pt(111) bimetallic surfaces with various thicknesses of deposited Ni, i.e., Ni_x/Pt(111) (x, Ni thickness in nanometer units), which were fabricated using molecular beam epitaxy at substrate temperatures of 343-473 K. The reflection high-energy electron diffraction (RHEED) patterns for the 343-K-deposited Ni_0.1nm-0.6nm/Pt(111) reveal Ni epitaxial growth on Pt(111). The CO exposure to the clean Pt(111) surface at 323 K engenders linearly bonded and bridge-bonded CO--Pt bands at 2093 and 1858 cm^-1. The 343-K-deposited Ni_0.1nm/Pt(111) gives rise to a new band at 2070 cm^-1 in addition to the CO--Pt(111) bands. The new band is most prominent for the Ni_0.3nm/Pt(111), on which the bridge-bonded CO on the Ni admetal layer appears at 1874 cm^-1. For the Ni_0.6nm/Pt(111), the 2070 cm^-1 band decreases in intensity and the bridge-bonded CO on the Ni admetal-layer dominates the spectrum, with accompanying weak absorption at 2035 cm^-1 caused by linearly adsorbed CO on the Ni layer. The low-energy electron diffraction (LEED) pattern for the 343-K-deposited Ni_0.3nm/Pt(111) shows incommensurate higher-order extra spots surrounding integer spots. In contrast, the incommensurate pattern changes to its original six-fold symmetry for the 473-K-deposited Ni_0.3nm/Pt(111). In contrast, the RHEED pattern for the 473-K-deposited Ni_0.3nm/Pt(111) revealed streaks having slightly wider separations than those for the clean Pt(111). The IRRAS spectrum for the 1.0-L-CO exposed 473-K-deposited Ni_0.3nm/Pt(111) reveals single-absorption at 2074 cm^-1. We discuss the CO adsorption behavior of Ni_x/Pt(111). [DOI: 10.1380/ejssnt.2009.230]