Starting from mesoporous V2O5 containing a small amount of Mg, V2O5/PANI (polyaniline) nanocomposites with lamellar and wormlike structures and fibrous morphologies were synthesized. Mesoporous V2O5/Mg was first prepared at room temperature using a binary mixture of surfactants (cetyltrimethylammonium bromide (CTAB) and hexadecylamine (HDA)) as a template and MgCl2 as an ordered structure stabilizer. After a heat treatment and solvent extraction which eliminated the surfactants, the as-synthesized mesostructured V2O5 was subjected to an in situ oxidative intercalation of aniline as polyaniline in the presence of air (V2O5 being the oxidation agent). The V2O5/PANI composite thus obtained kept an ordered mesostructure. The mesostructured V2O5 and V2O5/PANI nanocomposites were characterized by XRD, TEM, and BET/N-2 adsorption analysis. The FTIR of the mesostructured V2O5 and V2O5/PANI nanocomposites has demonstrated that PANI chains were intercalated into the mesostructured V2O5/Mg. The electrical conductivity of PANI/V2O5 nanocomposite reached values of the order of 10(-2) S/cm, which is by 5 orders of magnitude higher than that of the mesostructured V2O5/Mg. It was found that the aging in air facilitated the chain growth of PANI in the mesopores, thus increasing the electrical conductivity. It should be emphasized that the aging time needed to reach a relatively high conductivity of the mesostructured V2O5/PANI composites was shorter than those of the V2O5 xerogels/PANI. This occurred because the former possesses larger pores than the latter, and this facilitated the growth of the PANI chains.