Interfacial polarization model considers large interfacial polarization is key to electrotheological effect. In this Letter, high surface area mesoporous cerium-doped TiO2 electrorheological material is synthesized by using block-copolymer template in order to obtain large interfacial polarization. A very large enhancement in electrorheological activity is found for the first time in this nanoporous material. Its yield stress, over 70 kPa at 4 kV/mm electric field, is 100 times higher that of pure TiO2 and eight times higher that of single-doped TiO2 without mesopores. The large electrorheological improvement is attributed to enhanced interfacial polarization originating from high surface area of nanoporous structure. (C) 2004 Elsevier B.V. All rights reserved.