The present book foused on synthesis of conducting polymer- polyaniline ,Zinc Oxide nanoparticles, PANi-ZnO thin film nanocomposite and CSA doped nanocomposite of PANi-ZnO.The main focus is emphasized on fabrication of gas sensors working at room temperature. The materials were synthesized and characterized for structural, morphological, optical and electrical properties. Gas sensing characteristics were studied by exposing sensors fabricated to different reducing and oxidizing gases. Sensor performance parameters were calculated from response-recovery characteristics. Gas sensors developed were analyzed for their possible sensing mechanism through various characteristics studied for respective materials. Polyaniline showed maximum response of 23% to ammonia gas at room tempearture .The maximum gas response of 37 % was achieved with 78 % stability for ZnO films upon exposure of 100 ppm NO2 at operating temperature 200 °C.The maximum gas response of 14 % was achieved with 71 % stability for PANi-ZnO (50 wt %) sensor upon exposure of 100 ppm NH3 at room temperature.The maximum gas response of 28.11 % was achieved with 91 % stability for CSA doped PANi-ZnO at 100 ppm NH3 at RT.