Polyamide with side chain carboxylic acid la, which was the precursor polymer for polybenzothiazole, was mixed to obtain the precursor salt polymer 2a with the three armed tertiary amine in a mixture of benzene and N,N-dimethylacetamide (1:1). The solution was spread onto the water surface to prepare the L film of 2a. The LB film of 2a, which was successfully obtained with the Y type deposition, was converted to the LB film of polybenzothiazole (PET) 3a by heating at 280 C-. with removal of the tertiary amine. The FTIR and W-Vis absorption spectra, and the elemental analysis obtained by XPS proved the chemical structure of the PET LB film. The measurement of SAXS indicated the thickness of the precursor LB films was 2.9 nm, where the results of the ellipsometry were 2.8 and 0.34 nm for the precursor and PET LB films, respectively.