A porous nickel film was prepared by the selective anodic dissolution of copper from an electrodeposited Ni-Cu alloy film. A porous nanostructured nickel-based complex film electrode was further fabricated by oxidizing the obtained porous nickel film using cyclic voltammetry in 1 mol •L-1 KOH solution. The physical properties and pseudocapacitive performance of the as-prepared film electrodes were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electrochemical techniques. The results of SEM, XRD, and XPS indicate that the obtained complex film electrode consists of Ni, Ni(OH)2, and NiOOH, and it has a porous nanostructure. The electrochemical experiments revealed that the as-prepared porous nanostructured nickel-based complex film electrode had a specific capacitance of 578 F•g-1 at a current density of 20 A•g-1 at the initial cycle and it gave a specific capacitance of 544 F•g-1 after 1000 cycles with a capacitance retention of 94%. The nanoporous structure enhances the accessibility of the KOH electrolyte and promotes reactive species transport within the electrode. The nanoporous Ni substrate may improve the electronic conductivity of the thin Ni(OH)2 film at its surfaces. The nanosized Ni(OH)2 grains can shorten the proton diffusion pathways in the bulk of the solid nickel hydroxide. These factors are responsible for the superior pseudocapacitive performance of the porous nanostructured nickel-based complex film electrode.