We present an experimental and first-principles study to describe the changes in the electrical conduct i v i t y properties of the Emeraldine Salt (ES) form of polyaniline when using two different synthesis methods. The ES powders obtained by the interfacial synthesis method (PANI-I) exhibit higher electrical conduct i v i t y than that of the powders obtained by the conventional method (PANI-C). Investigation of the calculated band structure and density of states together with experimentally obtained optical-absorption spectra and the magnetic measurements indicate that PANI-I differs from PANI-C with respect to its localized defect state type which significantly alters the intrinsic conductivity . Furthermore, comparative studies of bond length , dihedral angles, and relative stabilities of Leucomeraldine Base, Emeraldine Base, ES Bipolaron state (ESB), and Polaron state (ESP) indicate that ESB and ESP states might coexist. Additionally, we confirm that increasing the length of the polymer chain to octamer in the unit cell does not influence the relative stability between ESB and ESP defect states.