This study deals with an adaptive friction compensator for asymmetric Coulomb friction in control systems. Generally, the Coulomb friction model is assumed to be symmetrical with direction of motion. However, it is no longer symmetric when a directional load is applied (i.e., transporting the load in direction to the force of gravity and so on). To improve the tracking performance in control system treating the directional load, the bias friction effect as well as the classical friction should be compensated. The proposed compensator estimates and compensates the bias Coulomb friction which consists of symmetric Coulomb friction coefficient and bias friction coefficient. Simulation results show the method can improve the performance of a control system.