This paper describes that the leaf spring damper (LSD) developed by authors can be controled by side clearance between side covers and leaf springs. The test rig and two prototype dampers with different side clearance were manufactured. Experiments were performed to investigate the effects of side clearance on the damping of the leaf spring damper. The stiffness and damping coefficients are obtained from the displacements and the reaction forces generated by rotating the eccentric shaft. All dynamic coefficients are plotted with the excitation frequency which is adjusted by rotating speed of the shaft.