We present the formation of polycarbazole (PCz) films at air–water interface by measurement of pressure-area isotherm and Brewster angle microscopy. The results suggest that PCz forms a very stable Langmuirmultilayer with liquid expanded character. PCz films were deposited on flexible bi-axially orientedpolyethylene terephthalate (BOPET) substrate by Langmuir–Blodgett technique. X-ray photoelectronspectroscopy results suggest that grown films are poorly doped (~12%). These films exhibit chemi-resistive response towards ppm level exposure of H₂S and NH₃ gases at room temperature. The typicalresponse times of these sensors at 10 ppm exposure of H₂S and NH₃ respectively are 3.44 min and 40 s.Modification of PCz films with Au (Au-PCz) resulted in a remarkable increase in the sensor response andselectivity towards H₂S over NH₃. Possible mechanism of response/selectivity improvement of Au-PCz towards H₂S has been discussed.