Adsorption behaviors of alkanethiol molecules are investigated on the surface of single-walled carbon nanotubes with vibrational spectrophotometer. Butanethiol (CASH), hexanethiol (C6H13SH), nonanethiol (C9H20SH), and dodecanethiol (C12H25SH) molecules are adsorbed on the nanotube surface, and infrared spectra are measured as a function of concentration of the adsorbed molecules and molecular chain length. Alkanethiol molecules are thought to be strongly adsorbed on the SWNT surface. The active adsorption sites in the nanotube surface are,thought to be Stone-Wales defects (5-7 ring defects). (C) 2004 American Vacuum Society.