Electrically conductive polycarbazole-titanium dioxide nanocomposite (PCz/TiO2) have been synthesized for the first time by in situ chemical oxidative polymerization of carbazole (Cz) in the presence of titanium dioxide (TiO2) nanoparticles. FTIR, SEM, TEM, XRD, TGA, and DTA were used to characterize PCz/TiO2 nanocomposites. The characterization results confirmed that there is a strong interaction between PCz and TiO2 nanoparticles and the nanocomposites showed higher thermal stability than pure PCz. The composite showed electrical conductivity and isothermal stability in terms of DC electrical conductivity retention under ambient condition below 100 degrees C. A nanocomposite-based sensor was fabricated for the detection of aqueous ammonia, it was found that the resistivity of the nanocomposites increases on exposure to ammonia at room temperature (25 degrees C), and it showed a linear relationship between the responses and the concentration of ammonia. The comperative antimicrobial activities of PCz, its PCz/TiO2-7 nanocomposite and ciprofloxacin drug with different bacteria have also been studied.