This paper presents an active suspension system for passenger cars, using linear and fuzzy-logic controls. The model is described by a nonlinear system with four degrees of freedom, subject to irregular excitation from a road surface. The active control is the sum of two kinds of control. The former is obtained by vertical acceleration of the vehicle body as the principal source of control, and the latter is obtained by using fuzzy-logic control as the complementary control. In the derivation of fuzzy control rules, linear combinations of the vertical and rotary velocities and displacements of the vehicle body are denoted as the input variables. The simulation results indicate that the proposed active suspension system proves to be very effective in the vibration isolation of the vehicle body.