Novel nanocomposite materials of conducting polyaniline (PANI) and Na+-montmorillonite ( MMT) were synthesized via a microemulsion polymerization. Microemulsions are macroscopically homogenous mixtures consisting of oil, water and surfactant. By investigating the X-ray diffraction analysis, we found that the d-spacing of the PANI/MMT nanocomposites became wider than that of pristine Na+-montmorillonite, showing that the PANI was successfully intercalated into the Na+-montmorillonite layers. FT-IR spectra of the nanocomposites also confirmed characteristic peaks of both PANI and MMT. SEM images of the PANI/MMT nanocomposite indicated that the polymerization occurs mainly between the clay layers. The room temperature dc conductivity of nanocomposites was studied.