Abstract: Under the presence of a constant magnetic field (0.2T), conducting polyaniline (PAn) was synthesized by microemulsion polymerization with sodium dodecylbenzenesulfonate (SDBS) as emulsifier, ammonium peroxydisulfate (APS) as oxidant and sulfosalicylic acid (SSA) as doping agent. The properties and structure of PAn were characterized by infrared spectrum, X-ray diffraction, particle-size analysis and conductivity measurement. The results indicate that the conductivity, doping ratio and corrosive potential of PAn are improved under the presence of magnetic filed, and no effect of magnetic field on the basic structural units of PAn is observed. Compared with the PAn synthesized under the absence of magnetic field, the PAn synthesized under the presence of magnetic field has a higher crystaUinity and obvious microscopic orientation structure, the polymerization time decreases from 3 to 2 h, the concentration of doped acid (C_SSA) decreases from 0.4 to 0.3 mol·L^-1, the mole ratio of SDBS and aniline monomer (n_SDBS/n_An) decreases from 0.6 to 0.45, and the conductivity of PAn increases from 6.42S·cm^-1 to 10.01 S·cm^-1.