Pt nanoparticles (Pt(n)) were prepared by chemical reduction method. The average dimension of Pt(n) is about 2.5 nm in diameter determined from TEM studies. The Pt nanoparticles were then self-assembled on massive Au substrate. The process of self-assembly was investigated with Fe(CN)(4-/3-)(6) for redox probe reaction. The result showed that the dithiol assembled on Au surface is inactive for electron transfer. However after assembly of Pt nanoparticles on the dithiol, the Au/SS-Pt(n) electrode becomes conductive again for electron transfer. The adsorption of CO on the Pt nanoparticles self-assembled on Au substrate in 0.1 mol x L(-1) H2SO4 was studied by using in situ FTIR reflection spectroscopy. IR absorption of linear and bridge bonded CO species was observed around 2030 and 1845 cm(-1) respectively. IR absorption of twin bounded CO adsorbed on the Pt nanoparticles was also observed about 2100 cm(-1). The results illustrated that the IR absorption of CO adsorbed on the Pt nanoparticles has been significantly enhanced. The present study is devoted to revealing the intrinsic properties of self-assembly system of nanoparticles, and is of importance in applications of electrocatalysis as well.