This paper reports a facile approach for fabricating core-shell structured graphene oxide (GO)-wrapped amine-modified poly(glycidyl methacrylate) (ami-PGMA) microspheres. The resulting core-shell structure is confirmed by scanning electron micsroscopy (SEM) and transmission electron microscopy (TEM), whereas the coexistence of GO and PGMA is confirmed by FTIR spectroscopy. The thermal stability of the ami-PGMA/GO microspheres is enhanced compared with that of pure PGMA microspheres. The novel ami-PGMA/GO composite microsphere-based electrorheological (ER) fluid shows typical ER characterization, using a rotational rheometer under an applied electric field. The dielectric analysis results along with the relaxation time and achievable polarizability of the fluid are correlated with the ER performance using a LCR meter.