Abstract: Composite self-assembled monolayers (SAMs) of poly (amide amine) generation 4.0 (PAMAM) and fatty acid on silicon were prepared. SAMs were characterized by ellipsometry, X-ray photoelectron spectroscopy and atomic force microscopy. The nano-tribological properties and micro-tribological properties were tested. Results showed that fatty acids (C18 and C12) were inserted successfully to the blank of PAMAM molecule in PAMAM SAMs. As a result, the friction force and friction coefficients of composite SAMs were decreased while the load-carrying capacity of the composite films was increased. The difference in molecular length of C18 and C12 fatty acids did not produce obvious difference in friction coefficients and load-carrying capacity