PPy@α-Al2O3 and PPy@CeO2 nanocomposites were synthesized free of acids by in situ polymerization and characterized by X-ray diffraction, scanning electron microscopy, differential scanning calorimetry and DC electrical conductivity measurements. X-ray diffraction pattern of Polypyrrole revealed a semi crystalline structure. The Le Bail method was performed using the X-ray diffraction pattern of polypyrrole and allowed the proposition of the unit cell parameters (P21/c, a = 9.0173 Å, b = 7.1641 Å, c = 6.4184 Å, α = 90°, β = 117.7°, γ = 90°), which is composed by a dimeric molecule disposed along the [001] direction. A cauliflower-like morphology was observed in polypyrrole, which consists of incomplete spheres forming nanoparticle clusters. Core-shell morphology was verified in the nanocomposites consisting of a thin layer of polymer reinforcement disposed over the metal oxides matrices. Differential scanning calorimetry measurements allowed verifying the hydrophobic behavior of the inorganic phase, promoting the repulsion of the internal water molecules out from the polymer phase. Then the initial decomposition temperature of the nanocomposites has become smaller. The polypyrrole electrical conductivity is lower than the nanocomposites and may be related with the absence of hydration water in nanocomposites and also to the surface conductivity due to the thin polymer layer. PPy@α-Al2O3 and PPy@CeO2 nanocomposites presented DC electrical conductivity 80% higher when compared to the as-synthesized polypyrrole. Thus, the aim of this paper was to characterize structural and morphologically the pure polypyrrole as well as the PPy@α-Al2O3 and PPy@CeO2 nanocomposites and correlate these results with the DC electrical conductivity measurements.