New nano-sized TiO2 electrorheological (ER) materials doped with different metal (M = Na, Zr, Ce, Al, Ca, Zn) oxides have been prepared. Relationships between the composition, microstructure, conductivity, dielectric property and ER effect of these materials have been studied. The results show that doping Na2O, ZrO2, Al2O3 or CeO2 can enhance the ER performance of the TiO2 material, whereas, doping CaO or ZnO would decrease the ER activity of the material. The shear stress (sE) of the suspension (25 wt%) of Na-doped TiO2 in dimethyl silicone oil reaches 1.6 kPa at the electric field strength E = 4.2 kV/mm and shear rate c = 300 s(-1), and its tau(r) value of 54.6 (tau(r) = tau(E)/tau(0), where tau(0) is the shear stress at no electric field) is seven times higher than that of pure TiO2 suspension. This high tau(r) value is very advantageous to the use. The dielectric loss tangent (tan delta) plays a dominant role in influencing the ER performance of a particle material, and the effect of the surface area (pore volume, especially) and grain size should be taken into account.