A series of density-controlled graphene oxide-coated mesoporous silica spheres (GO/SiO2) are successfully synthesized to investigate the influence of the particle density on electrorheological (ER) activity. The particle density of mesoporous silica spheres is controlled by creating different sized pores via surfactant template and swelling agent incorporation method. Additionally, ball-milled graphene oxide is successfully coated onto the surface of various silica spheres (SiO2) through amine-modification to enhance ER efficiency. In this study, we investigate that mesoporous silica spheres-based ER fluid (GO/ epSiO(2)) with lowest particle density exhibit most increased ER performance, which is 3-fold higher than that of similar sized neat silica spheres-based ER fluid (GO/nSiO(2)) without pore. In addition, the relationship between particle density, anti-sedimentation property, and ER performance is examined by applying Stokes' law and practical sedimentation observation. Furthermore, dielectric loss model is used to clarify the influence of dielectric property on ER activity. This newly designed ER study offers insight into the influence of the particle density on the performance of ER fluids. (C) 2014 Elsevier Inc. All rights reserved.