The characteristics of Couette flow of electrorheological fluid (ERF) between concentric cylinders is dependent on the parameter β, which is in the yield stress formula of ERF. In the case of β ＞ 2, the yield region locates between the yield surface and the outer cylinder. In the case of β ＜ 2, the yield region locates between the yield surface and the inner cylinder. When β=2, there is no yield surface. Steady and time dependent numerical results in relation to different β are presented and discussed.