4-(3-(4-((4-nitrophenyl)azo)phenyloxy)propyl)aminobenzene sulfonic acid (C3-ABSA) was designed and synthesized as a novel dopant of polyaniline (PANI). Structural characterization by FTIR, 1 H NMR and Second Ion Mass Spectrum (SIMS) showed that C3-ABSA has a molecular formula of C21H20N4 O6 S. Nanostructural PANI (e.g. nanorod or nanotube) was synthesized by a template-free method in the presence of C3-ABSA as a dopant. It was found that the size and room-temperature conductivity of the resulting PANI-(C3-ABSA) strongly depend on the synthetic conditions, in particular, nanotubes or nanorods with 50~300 nm in diameter and roomtemperature conductivity of 1.1 S/cm were obtained when water (1.0 mL) was added before polymerization. It was proposed that C3-ABSA plays a “template-like” role in forming PANI-(C3- ABSA) nanostructures due to surfactant function of C3-ABSA. The molecular structures were characterized by FTIR, UV-Vis. absorption and X-ray diffraction, showing the main chain and electronic structure are identical to the doped PANI, but exhibit partial crystallinity.