Abstarct: The introduction of chemical gas sensors in our environment is a process that started many years ago. However, although the process has been rather slow over the years, the interest for chemical gas sensors is rising due to the growing environmental awareness. The need to detect gas components in our surrounding is becoming more and more important as the technological levels increases in the world. The fabrication and improvement of the sensitivity and selectivity of gas sensors for detection of H2S gas have been the focus of this thesis. In this frxamework, we devoted particular attention to design of polymer baxsed nanocomposites and AC electrical measurements of the device (like capacitance and dissipation factor) on exposure to gas rather than resistance measurement. Two types of polymer nanocomposite baxsed on organic matterial, bromo-aluminum phthalocyanine, were synthesized as PPy/BrAlPc and PANi/BrAlPc to detect hydrogen sulfide gas. Gas sensing performance of the nanocomposite device PPy/BrAlPc results in fast response and good stability over the first 2 months to 100 ppm H2S gas by monitoring the changes in capacitance at the 1 kHz frequency. It produces 61% and 28% of the first response after 2 and 4 months, respectively which indicating lack of long-term stability. The performance of PANi/BrAlPc nanocomposite was investigated by making 8 sensors with different interdigitated electrodes to detect hydrogen sulfide gas. Much effort was spent on optimization of the design (interdigitated electrodes) and measurement parameters (like capacitance and dissipation factor) for the sensor when detecting different gas concentration. The obtained results show that the sensitivity of the PANi/ BrAlPc nanocomposite to detect hydrogen sulfide gas at various concentrations depends heavily on the applied frequency and shape of the interdigitated electrodes. The best performance for detecting hydrogen sulfide gas at various concentrations was obtained for spiral electrodes at a frequency of 1 kHz. It also has a good selectivity in detecting hydrogen sulfide gas between methane, ethanol and acetone.