Polyaniline (PANI) nanosphere with the dimension of 4 nm in diameter was successfully fabricated with octyltrimethylammonium bromide (OTAB) using microemulsion polymerization. The fabrication image of PANI nanoparticles was observed with TEM, and the synthesis was confirmed by FT-IR, Raman, and UV-Vis. The size of PANI nanoparticle could be controlled as functions of surfactant concentration, surfactant spacer length, and polymerization temperature. The diameter of the PANI nanosphere decreased with increasing surfactant concentratino and decreasing temperature. As the polymerization temperature decreased, the conductivity of PANI nanoparticle increased drastically. The tendency of conductivity was explained by the structure defects and crystallinity, which are characterized by EDAX analysis and XRD. The manetic carbon nanoparticles were also fabricated by carbonizing PANI nanoparticles. The fabrication of carbon nanoparticles was confirmed by Raman. The magnetic behavior was investigated by a super conducting interference device magnetometer.