Conducting polymers, such as polyaniline (PANI), polythiophene (PTh), polypyrrole (PPy), and their derivatives, have been used as the sensitive layers of gas sensors since early 1980s [1].Conducting polymers have gained popularity as important sensing materials for various organic vapors, hazardous gases, and humidity. They used as a material for fabricating sensor devices because of their applicability at room temperature. In comparison with most of the commercially available sensors, which are based usually on metal oxides and operated at high temperatures, the sensors made of conducting polymers have many improved characteristics. They have high sensitivities and short response time; particularly these features are ensured at ambient temperature [2]. The high conductivity is recognized to the more regular structure of the doped polymers like PANI. An additional advantage of PANI is that it can be made processable.