[en] Highlights: • Fe₃O₄@PPy core-shell nanoparticles were prepared by in-situ electropolymerization and electrodeposition method. • The Fe₃O₄@PPy nanoparticles possess satisfied dispersion property, acid stability, superparamagnetic behavior. • The saturation magnetization of the magnetic Fe₃O₄@PPy nanoparticles reached 43.5 emu/g. We report a facile method to synthesize polypyrrole-coated Fe₃O₄ core-shell magnetic nanoparticles (Fe₃O₄@PPy). First, crude Fe₃O₄ nanoparticles were synthesized by co-precipitation approach. PPy layers were generated and deposited on the surface of Fe₃O₄ via in-situ electropolymerization and electrodeposition, to construct core-shell structure nanoparticles. TEM observations showed the Fe₃O₄ nanoparticles changed from 15 nm to 120 nm in diameter after the PPy coating. The composition and morphology of Fe₃O₄@PPy nanoparticles were characterized by advanced spectroscopic and imaging techniques. The Fe₃O₄@PPy nanoparticles possess good dispersion property and acid stability in strong acid aqueous. The magnetic measurement at room temperature indicates that the Fe₃O₄@PPy nanoparticles exhibit superparamagnetic behavior, holding the saturation magnetization of 43.5 emu/g. All the results show great potentials of the Fe₃O₄@PPy nanoparticles in wide range of applications.