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In order to protect buildings and inner important facilities from damage caused by earthquakes, base Isolation system has been developed. In base isolation system, whole structure is set on elastomeric bearings called isolator. The main effect of the isolator is to decouple the structure from the ground and increase the resonant period of the structure to a value outside the range of periods containing the principal earthquake energy. There are two types of isolators. One is an isolator combined with damping function like a lead rubber bearing (LRB) and a high damping rubber bearing (HRB). The other is an isolator without damping function like a natural rubber bearing (NRB). The natural rubber bearing needs an energy dissipation device, when it is installed the seismic isolation system. In Japan many isolated building use the isolator and damper separately, and there are many types of dampers. The dampers are used as a part of the isolation system and are connected to the building in a similar manner as isolators. One end of the damper is fixed to the basement and the other is attached to the isolated superstructure. The lead metal is used as an energy dissipation device of seismic isolation system and vibration control system, because pure lead shows the characteristics of low stress yield, very high ductility and large plastic deformation. We introduce the basic characteristics of U-shaped lead damper and its ultimate performances. The U-shaped lead damper has the configuration of significantly bent and kinked column, thereby decreasing vertical tension forces that could be developed through geometrical nonlinearity combined with large horizontal deformation. The hysteretic behavior of the U-shaped lead damper shows the elastoplastic hysteresis loop, and this allows to provide high damping performance. However, the fatigue crack formation on lead damper is caused by small oscillation due to wind around the building or traffic vibration etc., though such fatigue crack has never been experienced during a big earthquake. According to the literatures, though it is obvious that the fatigue properties of lead can be improved by a vaseline-coating or a grease-coating on the specimen surface, its effect is not well understood qualitatively and quantitatively. To clarify the effect of coating, we carried out two type tests, very small deformation repeat tests under similar actual condition using the actual size U-shaped lead damper and rotating bending fatigue tests by using the pure lead specimens of round bar. According to these tests, a grease coating is identified as an effective method of fatigue life enhancement. We examine and discuss about these results and the environmental shielding effect by coating.