Vertically aligned iron oxide nanowire arrays were successfully synthesized via a cost-efficient maskless top-down approach. High density nanowires are formed by simple oxygen reactive ion etching of an iron-containing polymer film without any artificial mask. Highly crystalline hematite nanowires with a diameter of 38-45 nm and a high aspect ratio of 131 are uniformly produced over large areas after calcination. The high density graphene/magnetite nanostructure created by pyrolyzing iron oxide/organic nanowires with three-dimensional morphology provided highly enhanced Raman scattering with an enhancement factor of up to 7.0 x 10(4) due to trapping of the absorbed light in the three-dimensional graphene forest. Our maskless top-down approach to fabricate iron oxide nanowires offers unique advantages of a solution-based process to easily overcome the limit in the morphology and substrate-dependent properties of nanowire synthesis. This technique may have excellent practical potential as a simple, rapid, and reproducible process for the fabrication of high density and high aspect ratio iron oxide nanowires that are useful in various applications.