The formation process of a hemicyanine-terminated alkanethiolate self-assembled monolayer (SAM) on cold nanospheres immobilized on a class substrate was studied by absorption spectroscopy, optical second harmonic generation. and Monte Carlo simulation It was round that hemicyanine thiolate SAMs mainly for m in the upper hemisphere region of the gold nanospheres in the early stage, followed by the additional SAM formation in the lower region of gold nanospheres The hemicyanine SAM does not homogeneously form over the nanosphere surface and does not fully cover the nanospheres even alter long exposure to the hemicyanine solution This is because of the narrow space under the nanosphere, where the binding of the alkane disulfide to the gold sur face is considered to be a diffusion-controlled reaction The orientation of the hemicyanine molecules on cold nanospheres is similar to that of hemicyanine on a flat gold substrate These results are important to understand the SW face chemistry at nanostructure surfaces as well as the localized surface plasmon biosensing using metallic nanostructures