Three kinds of emulsifying agents have been used as emulsion droplets to prepare particle/emulsion complex electrorheological fluids (ERFs) to explore the effects of emulsifying agents on rheological properties. The rheological properties and microstructure of such ERFs have been examined, and a model of the complex chain for particle/emulsion complex ERFs has been given. Using emulsifying agents is an efficient way of improving the electrorheological effects in dry-based ERFs. There are three methods for emulsifying agents in ERFs: coating on the particle surface, dissolving in the continuous phase, and distributing in the continuous phase as droplets. This is determined by the interactions between the particles, emulsifying agents, and oil. For higher polarity emulsifying agents, the complex particles aggregate to form a bulk and cannot disperse in oil. For moderate ones, the complex particles disperse in oil and form complex chains or columns; the neighboring complex chain forms a network structure because of the rotation of the complex particles and displays a stronger electrorheological effect. With a lower polarity emulsifying agent dissolved in silicone oil, ERFs show lower electrorheological properties because of the decreasing mismatch of conductivity between the particles and continuous phase. (c) 2006 Wiley Periodicals, Inc.