A carbazole-containing amphiphilic Schiff base has been synthesized and was found to form a stable monolayer at the air/water interface. The monolayer can be fabricated into regular Langmuir-Blodgett (LB) film. The LB film shows acidichromism, i.e. when the LB film was exposed to HCl gas a color change was observed and consecutive exposing to NH3 gas the color was recovered. It has been confirmed by the UV-Vis spectra, fluorescence spectra and Fourier transform infrared spectra that such color change was due to the protonation of the imine group in the compound. In a mixed LB film of the compound with a copolymer (polyvinylidene chloride-co-polymethyl methacrylate), similar color change was observed upon photoirradiation. It was found that the acidichromism of the film was alternatively controlled by photoirradiation.