A tetrathiafulvalene derivative - tetrabenzylthiotetrathiafulvalene (TBT-TTF) - is a new material for a conducting Langmuir-Blodgett film. A 1:1 molar mixture with stearic acid was built up to obtain a conducting LB film. The conductivities of this mixed LB film were calculated from experimental results before and after iodine oxidation. To understand the increase in conductivity after iodine oxidation, the IR electronic absorption spectra and X-ray diffraction were investigated. The IR results suggest that the system undergoes continuous free chemical reactions after iodine oxidation. TBT-TTF forms the radical cation dimers associated with I-3(-). Finally, interaction of this new charge transfer complex (TBT-TTF)(x)(I-3(-))(1-x) (x < 1), gives rise to a new conducting LB film with the highest conductivity (4.7 x 10(-2) S cm(-1)). However, the conducting phase is unstable. The LB film can be oxidized repeatedly by iodine vapour. This is a possible application for gas sensors. The result of X-ray diffraction demonstrates that the molecular reorganization occurs because of tri-iodine chains in the bilayer.