Abstract: It is known that the robustness of the semi-active control law for Magnetorheological(MR)damper based on the conventional Linear Quadratic Gaussian(LQG)method is often poor. The Linear Quadratic Gaussian/Loop Transfer Recovery(LQG/LTR)technique is first employed to design a new semi-active control law with better robustness. The new semi-active control law for MR damper is obtained based on the LQG/LTR controller and the rule of maximal dissipating energy. Thus, the closed-loop system becomes insensitive to measurement noise and model parameter variation. A numerical example is presented to verify the semi-active control law. Simulation results show that the semi-active control law has better robustness and stability than that of the conventional LQG method.