Fe₃O₄@Au/polyaniline (PANI) nanocomposites were fabricated by in situ polymerization in the presence of mercaptocarboxylic acid. The mercaptocarboxylic acid was used to introduce hydrogen bonding and/or electrostatic interaction; it acts as a template in the formation of Fe₃O₄@Au/PANI nanorods. The morphology and structure of the resulting nanocomposites were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, x-ray diffraction and x-ray energy dispersion spectroscopy (EDS). It was found that the nanocomposites were rod-like with an average diameter of 153 nm, and they exhibited a core–shell structure. A UV–visible spectrometer, semiconductor parameter analyzer and vibrating sample magnetometer (VSM) were used to characterize the optical, electrical and magnetic properties of the Fe₃O₄@Au/PANI nanocomposites. It was interesting to find that these properties are dependent on the molar ratio of Au to Fe₃O₄ when the molar ratio of Fe₃O₄@Au to PANI is fixed. The magnetic property of the Fe₃O₄@Au/PANI nanocomposite is very close to superparamagnetic behavior.