Conductive polyaniline/cerium dioxide (PANI/CeO2) composites have been synthesized by in-situ polymerization of aniline in the presence of CeO2 nanoparticles. The structure and thermal stability of obtained composites were characterized by Fourier-transform infrared spectra (FTIR), Fourier-transform Raman spectra (FT-Raman), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The results showed that PANI and CeO2 nanoparticles were not simply blended, and a strong interaction existed at the interface of CeO2 and PANI. In the PANI/CeO2 composite, the degree crystallinity of PANI increased and diffraction pattern of CeO2 was amorphous. And that the composites were more thermally stable than that of the pure PANI. Electrical conductivity measurements indicated that the conductivity of PANI/CeO2 composites was much higher than that of the pure PANI and the maximum conductivity obtained was 11.68 S/cm at 17.5 wt% of CeO2.