Ultrafine nanoporous Cu was successfully fabricated through the dealloying of amorphous Ti₆₀Cu_40−xAu_x (x = 0, 1, 2 at%) ribbon alloys in 0.65 M HF solution under free immersion conditions. A bicontinuous nanoporous structure of Cu formed on Ti₆₀Cu₄₀, Ti₆₀Cu₃₉Au₁ and Ti₆₀Cu₃₈Au₂ ribbons with pore sizes of 134, 8.9 and 7.4 nm, respectively. The pore size of the nanoporous Cu dealloyed from Au-added alloys was more than one order smaller than that of the Ti–Cu alloy, which resulted from the 5-order decrease in the surface diffusivity through alloying of Au into Ti₆₀Cu₄₀ ribbons. The Au content increased rapidly during the dealloying process and eventually formed binary Cu–Au solid solution and Au nanoparticles. Modifying the surface diffusivity by adding Au made it possible for the formation of the ultrafine nanoporous Cu structure.