In this study, suspensions of core-shell particles dispersed in a silicone oil were fabricated and their rheological properties were evaluated at different external electric field strengths. The core-shell-structured composite materials were synthesized by coating poly(o-toluidine) (PoT) shells on the surfaces of silica particles. The silica particles were extracted from rice husk through acid and thermal treatments. The silica particles were then modified with (3-trimethoxysilyl)propyl methacrylate prior to the coating with the PoT shells. The chemical structures, morphologies, particle sizes, and elemental distributions of both silica and core-shell particles were investigated using scanning electron microscopy, Fourier-transform infrared spectroscopy, and energy-dispersive X-ray spectroscopy. Additionally, the rheological properties, chain formations, and dielectric properties of the suspensions were analyzed using rotational rheometry, optical microscopy, and an inductance-capacitance-resistance meter. The shear stress increased with the electric field strength along with the electro-rheological efficiency. The plot of the yield stress against the applied electric field strength exhibited a slope of 1.5. The fabricated core-shell particles are environment-friendly and are promising materials for applications in next-generation electro-rheological fluids.