Abstract: Damper is simply a shock absorber which is a spring or hydraulic device used in the vehicles suspension system. A car spring will extend and release the energy it absorbs from the bump at an uncontrolled rate if a damping structure is not present. The normal application of ER fluids is in fast acting hydraulic valves [10] and clutches. The other applications of ER are in brakes [6] and shock absorbers [5] which can be thought of as closed hydraulic systems where the shock is used to try to pump fluid through a valve. The vibration damper is also an essential part of the automobiles suspension system. Suspension system is the combination of various types of spring which include leaf springs, coil springs, shock absorbers, air springs and torsion bars. These are four sets of suspension springs in each vehicle. This paper is intended to express design considerations of ER damper for Land Cruiser. The purpose of the damper is to control spring and suspension movement. In this paper, the type of damper used is the twin-tube type applied with electrorheological fluid and nitrogen gas. The main purpose of this research paper is how to consider and design calculation of ER damper from the required known data such as piston diameter, rod diameter, ER liquid density, applied electric potential and moderate damper speed. This data had been applied in the design calculations. In this paper, it had been calculated the volumetric flow rate through the tube, the viscous pressure drop, shear damper force and damping force. From the calculated result, the shear damper force is 4 k Pa. The viscous pressure drop is 1.731 M Pa and damping force is 2270 N. In practical use, the damper force is in the range of 250-5000 N.