This thesis work is focused on the monolayer formation of phospholipid molecules and surfactants by Langmuir-Blodgett thin film technique on air/water or phosphate buffer interfaces. This study is also devoted to find out the effect of surfactants, the mixing ratio of the components, and also the phosphate buffer solutions on the monolayer films. The pH of the phosphate buffer solution that is used in experiments, is 7.2 and is coherent with the human blood plasma. In addition to this technique, a microscopic technique is employed. The monolayer features in different liquid interfaces are investigated by Brewster angle microscopy technique. In this study, the effect of ionic strength coming from the buffer solutions are examined in whole pure components and mixtures. It is aimed to find out to obtain more detailed information from the surface-pressure versus mean molecular area isotherms that are obtained from Langmuir-Blodgett technique. Therefore, the exact behavior of these organic thin films at the air/liquid interfaces are studied. The miscibility behavior and thermodynamic analysis of the mixed monolayers are also examined for each of the mixtures.