Silicon carbide is a key material in microwave (MW) processing and is widely employed as an MW absorber and catalytic agent. In this study, we experimentally improve the MW absorption properties of SiC particles at frequencies of 2.45 GHz by considering the shapes of fibers. We heated SiC fibers using MW radiation and their heating behaviors were then compared with their MW absorption properties. The heating behavior of the fibers was dependent on their aspect ratio; this result was in accordance with theoretical predictions. Furthermore, the mass ratio dependence of the MW heating behavior was investigated by employing an Al2O3-SiC fiber mixture. Their absorption properties exhibited peak MW absorption at specific relative densities under Emax and indicated different behavior from that predicted by the Maxwell-Garnett equation.