Adsorption of dicarboxylic acids [2-(trifluoromethyl)terephthalic acid and alpha,omega-dicarboxyperfluoroalkanes] from a solution onto a fluorine-terminated silicon(lll) [Si(lll)] surface was examined. X-ray photoelectron spectroscopy and Fourier transform infrared attenuated total reflection revealed that one carboxyl end covalently bonds to the Si surface, and the other end is exposed at the monolayer-air or monolayer-liquid interface. The reactivity of exposed carboxyl groups in the monolayer was confirmed by the fact that the surface species can be converted to chloroformyl groups by chlorination reagents.