Nanoporous Au−Pt alloys with pore- and ligament size down to few nanometers were fabricated by dealloying Ag−Au−Pt. Owing to the small structure size and large specific surface area, the surface stress and its variation give rise to significant stress and strain in the bulk of these materials. In fact, dilatometry experiments find electrochemical actuation with large reversible strain amplitude. The linear strain reaches ∼1.3% and strain energy density is up to 6.0 MJ/m3. The associated stresses may approach the elastic limit of the alloy.