Electrorheological (ER) elastomers, based on a gelatin hydrogel as matrix in which barium titanate ER particles are dispersed, were investigated. The behavior of particles was observed by a microscopic method. The ER effects of the elastomers are described with the compression modulus as a function of both particle concentration and intensity of the externally applied electric field. The result demonstrates that the particles were aligned in the matrix under an externally applied dc electric field. Furthermore, it was found that alignment of the particles increases the elastomer's modulus. In addition, both the chain effect and filler effect of the particles can dominate the modulus. The peak of modulus appears when using the elastomer with a particle weight fraction of 1.5% because of the complex dominations of the two effects. In like manner, the largest incremental modulus appears. Based on the results, we found that the modulus of the elastomer cured under an electric field is greater than that without an electric field, and increases with the increasing field. Thus ER behavior of the elastomer can be controlled by the electric field intensity. (C) 2004 Wiley Periodicals, Inc.