This work is an attempt to search for highly selective sensing material for 2-Chloroethyl ethyl sulfide (CEES, mustard gas simulant) vapors. Zeolite was modified with conducting polyaniline by the polymerization of anilinium cation. The nano composite of polyaniline/zeolite-Mor (Pani/Zeolite-Mor) was obtained by the chemical oxidative polymerization method. The polymer films and its composites with zeolite were used for detecting the toxic gas vapors. The sensing response of Pani and Pani/Zeolite-Mor was found to be 97.4 and 253.5 KΩ at 25 ppm of CEES. High sensing response of sensor was observed due to the zeolite framework, which provides greater pore volume and surface area. Pani/Zeolite-Mor sensor exhibited quick sensing response (11%) within 24 s at 25 ppm for CESS and relatively slower recovery (28.5 s) to the base line without heating. We also found that Pani/Zeolite-Mor show much higher response to CEES than NH₃, ethanol and HCN due to the presence greater no of electronegative atom (high dipole moment value) in the molecular structure of CEES than ethanol and HCN. Our results demonstrated that Pani/Zeolite-Mor sensor was selective to CEES. During experiment 36% humidity and 31 ˚C (±2) temperature was recorded inside the gas chamber. Sensor shows good stability (2 months), low cost and easy to fabricate. All synthesized samples were characterized by using XRD, FT-IR, SEM-EDX, TGA-DTA and BET techniques.