Growth of aligned and uniform α-Fe2O3 nanowire (NW) arrays has been achieved by a vapor–solid process. The experimental conditions, such as type of substrate, local growth and geometrical environment, gas-flow rate, and growth temperature, under which the high density α-Fe2O3 NW arrays can be grown by a vapor–solid route via the tip-growth mechanism have been systematically investigated. The density of the α-Fe2O3 NWs can be enhanced by increasing the concentration of Ni atoms inside the alloy substrate. The synthesized temperature can be as low as 400 °C. Fe3O4 NWs can be produced by converting α-Fe2O3 NWs in a reducing atmosphere at 450 °C. The transformation of phase and structure have been observed by in situ transmission electron microscopy. The magnetic and field-emission properties of the NWs indicate their potential applications in nanodevices.