Hollow carbon fibers were coated with Fe by chemical deposition to improve their electromagnetic performance. A parallel experiment was designed to investigate their chemical reactivity and surface curvature. The microstructure, composition, phase analysis and electromagnetic performance of Fe-coated and uncoated hollow carbon fibers were studied using SEM, EDAX, XRD and vector network analysis. The result indicates that magnetic loss is introduced due to the inherent property of iron. The real and imaginary parts of the complex permeability (μ′ and μ″) of the composites, which consist of the paraffin and the coated fibers after pretreatment and surface activity, are 1.44 and 0.54 at 2 GHz, respectively.