Polyaniline (PANI) was synthesized by the oxidation of aniline with ammonium peroxydisulfate (APS) as an oxidant in an immiscible organic/aqueous biphasic system, without added acid. An organic phase contained aniline dissolved in chloroform, while the oxidant was dissolved in water. The produced PANIs have conductivities in the range 0.008-0.1 S cm-1. Their nanogranular morphology was confirmed by scanning electron microscopy (SEM). Molecular structure of synthesized PANIs was investigated by FTIR, Raman, and UV-Vis spectroscopies, and elemental analysis. The influence of mechanical stirring and reaction time on the yield of polymerization, structure, and properties of synthesized PANIs was studied. The differences in the molecular structure, morphology, and conductivity between PANI prepared by dopant-free interfacial polymerization and PANI prepared by corresponding polymerization in monophasic aqueous system are discussed. The results are also compared with the literature data on the interfacial polymerizations of aniline with APS in the presence of acids.