To enhance the performance of electrorheological (ER) fluid, jellyfish-shaped p-phenylenediamine functionalized graphene oxide-g-polyaniline fiber (PPDG-g-PANI) nanocomposite particles were fabricated using an interfacial polymerization method. Their thermal stability was tested via a thermogravimetric analysis and their crystal structure, functional groups, and morphological image were examined using X-ray diffraction, Fourier-transform infrared test, and transmission electron microscope, respectively. The ER behavior of the nanocomposite particles was first directly observed using an optical microscopy with an electrical field. Flow curve and dynamic moduli of a PPDG-g-PANI-based ER suspension studied with a rotational rheometer for various electrical fields suggest that the composite shows typical ER behavior. The jellyfish-shaped PPDG-g-PANI composite particles also possess excellent sedimentation stability in silicone oil when compared with pure PANI fibers, thus showing a great potential for application in the field of smart materials. Dielectric spectra of the PPDG-g-PANI suspension were further tested using an LCR instrument.