For wider-band and stronger electromagnetic (EM) wave absorption, macroporous short carbon fibers/mullite matrix (C-f/Mu) composites were prepared via introducing short carbon fibers (0, 0.7, and 1.3 vol%) with length of 2-3 mm into macroporous mullite ceramic by gel-casting. The density of as-prepared C-f/Mu composites decreases from 2.93 g/cm(3)to 2.74 g/cm(3), while the porosity increases from 3.32% to 10.76% with the rise in carbon fibers content. The diameter of macropores in C-f/Mu composites is ranging from several microns to tens of microns. Complex permittivity and dielectric loss of the prepared composites in X-band (8.2-12.4 GHz) are significantly enhanced with increased carbon fibers content. The best EM wave absorption performance is obtained in the macroporous C-f/Mu composites containing only 0.7 vol% carbon fibers (C-f/Mu-0.7). The maximum absorption loss of C-f/Mu-0.7 is -38.3 dB at 12.08 GHz at the thickness of 2.1 mm, and effective absorption bandwidth below -10 dB (over 90% of EM wave absorption) covers the whole X band with the thickness of 2.35 mm. The results suggest that the C-f/Mu composites can be promising high-performance EM wave absorbing materials.