Antidot nanostructures were fabricated on Ni films by a single-step anodization process of magnetron-sputtered Al/Ni/W trilayers. Coercivity and saturation magnetization of the Ni layer were tuned by controlling the anodization time. Transmission electron microscopy was used to investigate the mechanism of the antidot formation process. The present study provides a simple and direct route for the fabrication of magnetic antidot nanostructures for device applications.