When electrotheological (ER) fluids are subjected to an electric field crossed with a shear flow, a large tilt angle of particle chains and a spin motion of ER particles can be observed. The particles spin even inside the field-induced tilt chains. In certain range of shear rates, the chain tilt angle (between the particle chain and electric field) is beyond those predicted by some existing theoretical models. We further present an improved theory to understand the experimental observations. (c) 2005 Elsevier B.V. All rights reserved.