The self-assembly of hexadecyltrimethylammonium bromide (C16TAB) and dodecyltrimethylammoniumbromide (C12TAB) from ethanol solution that was allowed to evaporate was imaged on graphite with ascanning tunneling microscope (STM). The STM images showed that these cationic surfactants could formordered parallel stripes with approximately twice the length of a surfactant molecule, displaying that thecationic surfactants were arranged in a head-to-head configuration. The high-resolution image indicatedthat three bright spots amid a stripe could correspond to three methyl groups of a couple of head-to-headmolecules. This observation provided direct support for interpretation of the model proposed from atomicforce microscope studies concerning the first adsorbed layer at solid−aqueous interfaces.