In this paper, the uniform and ordered polyaniline nanoparticles with the average diameter about 95 nm were electropolymerized in solution containing 0.2 mol dm(-3) aniline and 1.2 mol dm(-3) HCl using the method of constant potential at 0.7 V in the presence of magnetic field (780 mT). Effects of the material of substrate and time on properties of polyaniline film were investigated. The experimental results show the magnetic field has orientation effect on aniline polymerization. Distinct scanning electron microscope (SEM) morphologies show polyaniline nanoparticles can be formed in the presence of the magnetic field. The CV and ac impedance results indicate the magnetic field makes the polymer film redox current larger and the charge transfer resistance (R-ct) smaller. The nanoparticles were characterized by FTIR spectra, UV-vis spectra. (c) 2007 Elsevier B.V. All rights reserved.