Intercalation of polymers in clay layers has been widely accepted as the most advanced method to synthesize nanophase organic-inorganic hybrids. Here, the clay consists of both anionically charged layers of aluminum/magnesium silicates and small cations such as sodium or potassium located in silicate interlayer galleries [1]. These silicate layers exchange organic cation molecules and swell under certain solvents. Thereby, the polymer solution intercalation method is based on a solvent quality, i.e., whether the polymer is soluble and the silicate layers are swellable [2]. The driving force for polymer intercalation into a layered silicate from solution is the enthalpy gained by desorption of solvent molecules, which compensates for the entropy loss due to the confinement of intercalated chains [3]. Polyaniline (PANI) is one of the best known conducting polymers for commercial applications, because of its environmental stability, good processability, and relatively low cost. However, it contains large equilibrium polylene rings with torsional displacement out of the plane defined by the ring bridging atoms (amine/imine nitrogens). Because of the stiffness, it is very difficult to dissolve the PANI in common organic solvents. However, PANI’s derivatives including substituent groups (−CH3,−OCH3 or −OC2H5) in monomer or polymeric chain show an excellent solubility in various organic solvents. Despite of its lower conductivity than that of PANI, the poly(o-ethoxyaniline) (PEOA) substituted with —OC2H5 in PANI has attracted much attention due to its good solubility and corrosion resistance in metallic surfaces [4]. The conducting polymer/clay nanocomposite system has also been used not only to enhance the processability (colloidal stability or mechanical strength) [5, 6] but also to improve physical properties. Polypyrrole/montmorillonite (MMT) nanocomposites were synthesized by an emulsion polymerization using dodecylbenzene sulfonic acid [7], and PANI/clay nanocomposites [5, 8, 9] have been reported to improve physical properties including electrical conductivity and electrorheological performance. In the work reported in this letter, we synthesized soluble PEOA and prepared PEOA/clay nanocomposites. Here, the organic clay was a natural MMT modified with a quaternary ammonium salt of dimethyl, hydrogenated tallow, 2-ethylhexyl quaternary ammonium. Characteristics of PEOA/clay nanocomposites were investigated for two different compositions of the PEOA. Electrical conductivity can be controlled by the clay contents in the intercalated PEOA/clay nanocomposites. At first the PEOA, as a soluble conducting polymer in organic solvent, was synthesized. A 0.6 mol ethoxyaniline monomer (Aldrich, USA) in 4 × 10−4 m3 of 1 M HCl was stirred for 2 h, and the polymerization was initiated at 25 ◦C by adding a solution of 0.36 mol ammonium persulfate as an oxidizing agent in 2.4 × 10−4 m3 of 1 M HCl. Products of PEOA (pH = 1) were dried at 25 ◦C for 2 days using a vacuum oven. The organic clay (OMMT), Cloisite 25A (Southern Clay Product, USA), was swollen in chloroform for l day. The PEOA particles were simultaneously dissolved in chloroform. Fixed amounts of clay and PEOA in chloroform solutions were mixed together and stirred for 1 day. This mixed solution was filtered and dried at 25 ◦C for 2 days using a vacuum oven. The powder form of the products was obtained. Fourier Transform Infrared (FT-IR) spectroscopy (Perkin Elmer System 2000) was used to identify the chemical structure of the PEOA which was prepared as a disk, dispersed in KBr. The intercalation of PEOA/clay nanocomposite was examined via transmission electron microscpoe (TEM) (CM 200, Philips). The X-ray diffraction (XRD) measurement, using the Rigaku DMAX 2500 (λ = 0.154 nm) diffractometer, was also performed. The conductivity of PEOA particles and nanocomposites was measured with a pressed disk of polymer using a 2-probe method with silver electrodes on each side [7]. The pellets of PEOA particles were prepared using a 1.3 × 10−2 m KBr pellet die, and the pellet resistance was measured using a picoammeter (Keithley model 487, Cleveland, USA) with a conductivity cell. The conductivity (σ ) was then obtained from the following Equation 1,