We have studied the formation of aggregates of a TTF derivative (tetrakis(octadecylthio)tetrathiafulvalene) in solution and in Langmuir-Blodgett films. It has been found that the monolayer formation of the TTF derivative was dependent upon the concentration of the spreading solution and also on the maximum spreading area. The floating monolayers were not stable at the air-water interface. However, stable mixed monolayers could be formed by adding behenic acid. The surface pressure vs area isotherms at several molar fractions of the components were measured. A molecular reorganization of the molecules during the compression may be observed. The mixed films were formed on quartz and CaF2 substrates for W-vis and IR studies.