A simple co-precipitation route was developed to synthesize uniform core–shell structured calcium and titanium precipitation (CTP) particles with ideal morphology and no aggregation. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), and interface tension/contact angle (CA) measurement were utilized to characterize the components, structure, morphology, and wettability of the SiO₂–CTP materials. The obtained core–shell structural SiO₂–CTP particles were well dispersed spherical nanoparticles with a narrow size distribution. The electrorheological (ER) properties were studied by the shear stress under various electric fields. The SiO₂ (2.3 wt%)–CTP ER fluid showed notable ER activity with a shear stress of about 109 kPa (at 5 kV mm⁻¹), which outclassed the shear stress (65 kPa) of the CTP ER fluid. The ER properties of samples can be tuned by a few factors in the experimental process, such as the concentration of SiO₂ particles and citric acid, pointing out the great potential for application of this route in bulk synthesis of many other types of ER materials.