Poly(2-chloroaniline)/silica (P2CIAn)/SiO2 nanocomposites have been chemically prepared by oxidative polymerization of 2-chloroaniline in acidic medium containing SiO2. The prepared composites were characterized by FTIR, UV-vis, TGA, XRD, SEM, ESEM, conductivity, and magnetic susceptibility. The incorporation of P2CIAn in composites was endorsed by FTIR studies. The effect of the solution concentration of P2ClAn and P2CIAn/SiO2 prepared in protonated, deprotonated, and reprotonated structures on the UV-vis spectra was investigated into three different solvents (DMF, NMP, and H2SO4). In all forms, the oxidation state of P2CIAn and P2CIAn/SiO2 composite increased with increasing concentration of the testing solution into H2SO4. Thermogravimetric study exhibited that the composite has a higher thermal stability than P2CIAn. XRD measurement of the composite revealed that the crystal structure of incorporated SiO2 undergone a distortion and converted into amorphous. Thus, the XRD pattern of P2CIAn was predominant. SEM analysis results revealed interesting morphological features for the composites converted to different forms and confirmed the formation of monodispersed composite particles. ESEM image of P2ClAn/SiO2 has particle diameter of less than 1 mu m. The conductivity of P2CIAn and P2CIAn/SiO2 was measured by four-probe technique. Magnetic susceptibility measurements revealed that the composite has a paramagnetic properties. (c) 2006 Wiley Periodicals, Inc.