The adsorption and desorption of butanethiol (CH3(CH2)(3)SH: C4), hexanethiol (CH3(CH2)(5)SH:C6) and octanethiol (CH3(CH2)(7)SH: C8) on Au (1 1 1) under vacuum condition have been studied by temperature programmed desorption (TPD). Desorptions of thiolate radical species were observed for C6 and C8. Connecting the desorption temperatures of parent thiols from the first layer and that of hydrogen, we were able to find a condition for thiolate radicals to be desorbed from the surface.