The three-dimensional structures of emeraldine base polyaniline (PANI) and (polyaniline)0.5V2O5·1.0H2O have been determined by total X-ray scattering experiments. Atomic pair distribution functions (PDF) were measured to obtain experimental observables against which structural models were tested and refined. The PDF approach is necessary because of the limited structural coherence in these nanostructured materials. Polyaniline possesses a well-defined local atomic arrangement that can be described in terms of an 84-atom orthorhombic unit cell. The nanocomposite (PANI)0.5V2O5·1.0H 2O too is locally well ordered and may be described in terms of a small number of structure-sensible parameters. The PDF approach allows the construction of structure models of PANI and (PANI)0.5V 2O5·1.0H2O on the basis of which important materials' properties can be explained predicted and possibly improved.