We report a comparative study of the structure and frictional properties of self-assembled monolayers (SAMs) generated by the adsorption of three homologous 17-carbon alkanethiols-heptadecanethiol, 2,2-dipentadecyl-1,3-propanedithiol, and 2-pentadecyl-1,3-propanedithiol-onto the surface of Au(lll). The structural properties of these SAMs were characterized by atomic force microscopy, surface infrared spectroscopy, X-ray photoelectron spectroscopy, spectral ellipsometry, and wettability by water and hexadecane. The frictional properties of the SAMs were examined by friction force microscopy. The results demonstrate that the packing density and the related crystalline order of the hydrocarbon chains influence the frictional properties of organic thin films. The origins of the frictional differences measured from these films are discussed in terms of the structure of the films.