Mixed self-assembled monolayers (MMLs) were prepared by exposing mica to (i) a solution of octyltrichlorosilane and 2,2,2-trifluoroethyl 11-(trichlorosilyl)-undecanoate in toluene and (ii) an aqueous solution of decamethonium bromide and dodecyltrimethylammonium bromide. X-ray photoelectron spectroscopy, atomic force microscopy, and contact angle measurements were used to examine the composition, the thickness, the smoothness, and the stability of the self-assembled layers in different solvents. For both types of MMLs, we report the experimental conditions under which smooth mixed monolayers with a well-defined composition can be obtained. In silanization experiments, the ratio of silane species in the mixed layer was close to that in the solution, and the MMLs obtained from positively charged amphiphiles exhibited strong surface enrichment with dodecyltrimethylammonium bromide.