Abstract： Semi-active control algorithm for MR damper based on adaptive fuzzy control (AFLC) is proposed in this paper for dealing with nonlinearity and uncertainty of structure and external loadings. Equivalent control law is approximated by the adaptive fuzzy control system by adjusting the membership functions of conclusion part in rules on line. Lyapunov stability theorem is employed to design the adaptive law. AFLC is integrated with clipped optimal control algorithm for MR damper. Benchmark control problem for a seismically excited highway bridge developed recently is simulated, results show that active and semi-active control strategy based on AFLC reduce response quantities of structure effectively when suffered to seismic loadings with different soil type and different amplitude, semi-active achieve almost the same control performance of active control, this superiority promises a very high value in popularization and application of MR semi-active control strategy.