Alkanethiol-protected Au nanoparticles have been chemically immobilized on Au(111) substrates by alkanedithiol and alkanethiol mixed self-assembled monolayers (SAMs). Octanethiol SAMs on Au(111) have been used as host matrices for molecular insertion by 1,8-octanedithiol (C8S2) and 1,10-decanedithiol (C10S2). The dithiol molecules in the mixed SAMs and the Au nanoparticles on the mixed SAMs were observed by scanning probe microscopy. Thedensities of C8S2 and C10S2 mixed SAMs were controlled by varying the dithiol concentration from 0.5 to 50 mM. The densities of Au nanoparticles were almost equal to those of the dithiol molecules, indicating that the Au nanoparticle chemisorbed through the protruding sulfur of the dithiol molecules displaced the protecting group of the Au core. The chemisorbed Au nanoparticles were stable for scanning tunneling spectroscopy (STS) measurements. The resistance of the chemisorbed nanoparticles between the Au core and the Au(111) substrate is discussed. (C) 2009 The Japan Society of Applied Physics