The release of ethylene gas from agricultural products such as fruits, vegetables, and flowers during storage and transportation is the main cause of blooming of flowers and ripeness of fruits before their ripening phase. The ethylene gas acts as hormone plant leading to a decrease in the life time of agricultural products and a deterioration of product value. The continuous development of ethylene gas sensor is needed to increase an efficiency in detection and indicating life time cycle of agricultural products. The aims of this research were to fabricate ethylene gas sensor based on polyaniline/multiwall carbon nanotube (PANi/MWCNT) composites and to investigate the effect of MWCNT content on an improvement of its sensitivity. The sensitive layer for ethylene sensor was electrochemically synthesized from aniline in acid aqueous solution with different amounts of MWCNT. With cyclic voltammetry method, the sensitive layer of PANi/MWCNT was electrochemically synthesized via an in situ radical polymerization by repeating potential cycling in the range of -0.3 to 1.0 V relative to the silver reference electrode and platinum counter electrode. The response of these composite films for ethylene gas was evaluated by monitoring the change in electrical resistance at room temperature. After three month aging, the results revealed that the PANi/MWCNT composite films had higher response than pure PANi film and can be responded ethylene gas as lower as 10 ppm. The PANi/MWCNT composite films were characterized by fourier transform raman spectroscopy (FT-RAMAN). Thermal behaviors of PANi-MWCNT composite films were investigated by thermogravimetric analyzer (TGA). The morphology of PANi/MWCNT composite films were investigated by scanning electron microscope (SEM).