According to the dielectric design, a new kind of rare-earth (RE)-doped TiO2 particle was synthesized by means of sol-gel technique for use in electrorheological (ER) fluids. A distinct enhancement in the yield stress under dc electric field was found by using such particles, when compared with that of pure TiO2. The yield stress of typical cerium-doped TiO2 suspension was about 5.0 kPa at 3 kV/mm and 7.0 kPa at 4 kV/mm, which were 10 times higher than that of a pure TiO2 suspension. The yield stress showed a marked dependence on RE-doping degree. Substitution of 10mol% cerium or 8mol% lanthanum for Ti could obtain the highest yield stress. These were well explained by the dielectric measurements that showed an increase in the dielectric loss and the dielectric constant at low frequency and their regular change with rare earth content. The lattice distortion and defects in the TiO2 crystal caused by substitution for Ti with large-radius RE ions may be responsible for the obvious improvement noted above.