Abstract: The effects of magnetic field annealing on the properties of Fe48Co52 alloy nanowire arrayswith various interwire distances (Di=30-60 nm) and wire diameters (Dw=22-46 nm) wereinvestigated in detail. It was found that the array's best annealing temperature and crystalline structure did not show any apparent dependence on the treatment of applying a 3 kOe magnetic field along the wire during the annealing process. For arrays with small Dw or with large Di, the treatment of magnetic field annealing also had no obvious in°uence on their magnetic performances. However, such a magnetic field annealing constrained the shift of the easy magnetization direction and improved the coercivity and the squareness obviously for arrays with large Dw or with small Di. The difference in the intensity of the effective anisotropic field within the arrays was believed to be responsible for this different variationof the array's magnetic properties after magnetic field annealing.