Self-assembled monolayers (SAMs) of amphiphilic organic molecules that form on a solid surface have generated an enormous amount of interest in interdisciplinary research areas as diverse as molecular engineering of surfaces, tribology, biology, nanotechnology, polymer composites, organic electronics, and analytical chemistry. We measured the contact angle to study the surface chemistry and structures of SAMs. Octadecylphosphonic acid (OPA) has the featureof being able to form a monomolecular film in an extremely short time (i.e., within several seconds). The analytical approaches developed in this study should be applicable to research and development related to controlling surface properties.