Recently, electro-active composites have been considered by several researchers because they exhibit an interesting change in their viscoelastic properties under an applied electric field. However, their relative elastic modulus change ΔG′ = G′(E) − G′(0) is still low and rarely exceeds 100 kPa. In this article, we demonstrated that, by synthesizing mesoporous aggregates of titanium dioxide (TiO₂) and by adsorbing acetylacetone dipolar molecules (Acac) onto the TiO₂ surface, the TiO₂-Acac/PDMS electrorheological elastomer achieved a relative elastic modulus change ΔG′ higher than 500 kPa for an applied electric field of 2 kV mm⁻¹. The dependence of the electrorheological response of TiO₂-Acac/PDMS on the DC electric field strength, AC electric field frequency and shear strain magnitude was discussed regarding the conductivity ratio and permittivity ratio between doped TiO₂ semiconducting particles and the PDMS matrix. The high electrorheological performance of TiO₂-doped Acac as semiconducting particles filled in the elastomeric matrix makes this kind of material a promising candidate for application in the automotive industry, robotics, vibration isolators, building applications or electro-active actuators.