A new Schiff base containing carbazole group (CzSB) was synthesized. Although the compound can not form stable monolayer at air/water interface itself, it does form stable monolayers by mixing with stearic acids as verified from the surface pressure area measurements. The mixed monolayers can be deposited by vertical dipping method. UV Spectroscopic studies of the mixed LB films reveal a broadening and red shift of the absorption spectra compared to those of CzSB in the ethanol solution, which confirms the formation of organized aggregates of the compounds in the mixed LB films. An ordered LB film was obtained as confirmed by using low angle X ray diffraction. The mixed LB film shows acidichromism, that is, the colors of the LB films can be reversibly changed upon exposing to HCl and NH 3 gas alternatively. On the basis of FT IR measurement, it is proposed that the protontation of the imine group in the compound is the reason for the acidichromism. A new Schiff base containing carbazole group (CzSB) was synthesized. Although the compound can not form stable monolayer at air / water interface itself, it does form stable monolayers by mixing with stearic acids as verified from the surface pressure area measurements. The mixed monolayers can be deposited by vertical dipping method. UV Spectroscopic studies of the mixed LB films reveal a broadening and red shift of the absorption spectra compared to those of CzSB in the ethanol solution, which confirms the formation of organized aggregates of the compounds in the mixed LB The ordered LB film was obtained as confirmed by using low angle X ray diffraction. The mixed LB film shows acidichromism, that is, the colors of the LB films can be reversibly changed upon exposing to HCl and NH3 gas alternatively. On the basis of FT IR measurement, it is proposed that the protontation of the imine group in the compound is the reason for the acidichromism.