Magnetic Fe3O4-poly(aniline-co-o-anthranilic acid) nanoparticles were prepared by a novel and simple method: anthranilic acid assisted polymerization. The synthetic strategy involved two steps. First, Fe3O4 nanoparticles capped by anthranilic acid were obtained by a chemical precipitation method, and then the aniline and oxidant were added to the modified Fe3O4 nanoparticles to prepare well-dispersed Fe3O4-poly(aniline-co-o-anthranilic acid) nanoparticles. Fe3O4-poly(aniline-co-o-anthranilic acid) nanoparticles exhibited a superparamagnetic behavior (i.e., no hysteresis loop) and high-saturated magnetization (M-s = 21.5 emu/g). The structure of the composite was characterized by Fourier-transform infrared spectra, X-ray powder diffraction patterns, and transmission electron microscopy, which proved that the Fe3O4-poly(aniline-co-o-anthranilic acid) nanoparticles were about 20 nm. Moreover, the thermal properties of the composite were evaluated by thermogravimetric analysis, and it showed excellent thermal stability. (c) 2006 Wiley Periodicals, Inc.