A series of polymer-clay nanocomposite (PCN) materials that consisted of emeraldine base of poly(o-ethoxyaniline) (PEA) and layered montmorillonite (MMT) clay were prepared by effectively dispersing the inorganic MMT clay platelets in organic PEA matrix via in situ oxidative polymerization. Organic o-ethoxyaniline monomers were first intercalated into the interlayer regions of organophilic clay hosts and were followed by a one-step oxidative polymerization. The as-synthesized PCN materials were characterized by Fourier transform infrared (FTIR) spectroscopy, wide-angle X-ray diffraction (XRD) and transmission electron microscopy (TEM). PCN materials at low clay loading up to 3 wt% in the form of coating (e.g. 0.5 wt%) on cold-rolled steel (CRS) were found to exhibit much superior corrosion inhibition effect as compared to those of the bulk PEA by performing a series of electrochemical measurements of corrosion potential, polarization resistance, corrosion current and impedance spectroscopy in 5 wt% aqueous NaCl electrolyte. Furthermore, it was found that a further increase of clay loading up to 3 wt% results in a slightly enhanced molecular barrier property of PCN materials. The molecular weights of PEA extracted from PCN materials and bulk PEA were determined by gel permeation chromatography (GPC) analysis with NMP as eluant. Effects of the material composition on the molecular barrier, thermal stability, electrical conductivity and optical properties of PEA along with a series of PCN materials, in the form of free-standing film, fine powder and solution, were also studied by molecular permeability measurements (GPA), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), four-point probe technique and UV-vis spectra.