The effects of frequency, volume fraction of carbon black, and porosity on electromagnetic and electromagnetic were absorbing properties of an epoxy-carbon black composite were investigated. The complex permeability, permittivity and electromagnetic attenuation values of the composite were obtained using a network analyzer in the frequency ranges from 50 MHz to 10 GHz. In the carbon black epoxy composite, the frequency dispersion behaviors of the complex permittivity changed from resonance spectrum to relaxation spectrum with decreasing she amount of carbon black. The complex permittivity of the composite increased with decreasing the porosity. In the volume fraction leading the resonance spectrum, the electromagnetic attenuation characteristics were determined by the material constants below the resonance frequency. On the other hand, in the volume fraction leading the relaxation spectrum the electromagnetic attenuation characteristics were determined by the material constants above the relaxation frequency. In case of the composite exhibiting resonance behavior, when the frequency became higher than the resonance frequency the electromagnetic attenuation behavior was independent on the thickness of the material.