In this paper, numerical aspects of a sensitivity control for the semi-active suspension system with a magnetorheological (MR) damper are investigated. A 2-dof quarter-car model together with a 6th order polynomial model for the MR damper are considered. For the purpose of suppressing the vertical acceleration of the sprung-mass, the square of the vertical acceleration is defined as a cost function and the current input to the MR damper is adjusted in the fashion that the current is updated in the negative gradient of the cost function. Also, for improving the ride comfort, a weighted absolute velocity of the sprung-mass is added to the control law. The implementation of the proposed algorithm requires only the measurement of the relative displacement of the suspension deflection. The local stability of the equilibrium point of the closed loop nonlinear system is proved by investigating the eigenvalues of the linearized one. Through simulations, the passive suspension, the skyhook control, and the proposed sensitivity control are compared.