Bulk nanoporous platinum (np-Pt) samples with a remarkably fine ligament size down to 2 nm and good mechanical robustness were fabricated for the first time by electrochemically dealloying Pt₁₅Cu₈₅ master alloy in 1 mol L⁻¹ H₂SO₄ at 60 ℃. The as-prepared np-Pt shows an electrochemically active specific surface area as high as 25 m²/g due to the ultrafine nanostructure. The active surface area remains almost invariable even after 15% macroscopic compressive strain. Furthermore, np-Pt shows considerably high thermal stability due to the low surface diffusivity of Pt. Np-Pt is a promising surface- or interface-controlled functional material, particularly when excellent electrochemical and mechanical performance are necessary due to its high surface-to-volume ratio and mechanical robustness. This work demonstrated the potential application of np-Pt as an electrochemical actuation material. In-situ dilatometry experiments revealed that the surface adsorption–desorption of OH species on np-Pt causes significant strain variations. The proposed np-Pt electrochemical actuator shows an operating voltage down to 1.0 V, a large reversible strain amplitude of 0.37%, and a strain energy density of 1.64 MJ/m³.