Using activated carbon as templates, Ni coated activated carbon powders were prepared by electroless nickel-plating method. Removing the activated carbon templates, nickel hollow powders were prepared. The prepared Ni coated activated carbon powders and nickel hollow powders were characterized by means of X-ray diffraction (XRD), scanning electron microscope (SEM), and Field emission scanning electron microscope (FESEM). The results show that most of the activated carbon template could be eliminated at 210 degrees C in air or at 700 degrees C in nitrogen without oxidation of most of the coated nickel. The Ni hollow powders heated in air showed more porous than that of annealed in nitrogen. The dielectric and magnetic loss of Ni hollow powders -paraffin wax composites were measured in the frequency range of 2-15 GHz by reflection/transmission way using network analyzer. The reflection coefficient of Ni hollow powders-paraffin wax absorbers with 2 mm thickness was calculated by transmission line theory, the maximum reflection loss can be up to - 16 dB. (c) 2007 Elsevier B.V All rights reserved.