The emulsion film has become the focus of the study of emulsion because the film stability and structure play a crucial role on the whole stability and structure of emulsions. In this study, the single emulsion film stabilized by tetradecyltrimethylammonium bromide (C14TAB) in dodecane phase has been investigated thermodynamically. In order to make clear the theoretical treatment, it has been reviewed how the thermodynamic quantities of extremely thin films are defined and how it is related to the experimental variables such as temperature, pressure, and concentrations of solutes. By using the equations demonstrated here, the film tension and film surface tension, which were evaluated from the measurement of contact angle between the emulsion film and the surrounding bulk meniscus, have been inspected thermodynamically from the viewpoint of the influence of added salt (KBr) concentration on the structure of thin emulsion film. In addition, the comparison of the results obtained has also been made between the foam and emulsion films to reveal the effect of an ambient dodecane phase on the properties of the film.