A series of polyacrylonitrile-based hollow-porous and solid carbon fibers were prepared by pyrolysis of polyacrylonitrile-based hollow-porous and solid fibers at the same condition. The microstructure, composition, surface electrical conductivity, electromagnetic parameters and reflectivity of carbon fibers were studied. The microwave absorbing properties of two kinds of carbon fibers as microwave absorbents were parallel investigated. Results show that the apparent density of the hollow-porous carbon fibers is lower than that of the solid carbon fibers due to their hollow-porous structure. The surface electrical conductivity of single solid carbon fiber is nearly 10 times that of the hollow-porous carbon fiber. The -10dB bandwidths of solid carbon fiber composites carbonized at 850 and 950°C are both 0GHz, while those of the corresponding hollow-porous carbon fiber composites are up to 3.05 and 2.62GHz, respectively. Results indicate that the microwave absorbing properties of the hollow-porous carbon fiber composites are better than those of solid carbon fiber composites.