High-speed superplasticity has been realised at room temperature for the first time with a nano-crystalline Zn-Al alloy. Zn-Al alloys have some advantages over low-yield-point steels in their low work-hardening rate and high ductility. In addition, Zn-Al alloys are environment-conscious because of no harmful metal like Pb. However, when Zn-Al alloys are subjected to plastic deformation, the strain is localised and local fracture can take place because of their low work-hardening property. In this study, a seismic damper was designed with a nano-crystalline Zn-Al alloy. As a result, an ecological and high performance seismic damper, the so-called "maintenance-free seismic damper", has been successfully developed.