The uniform ultra-long SiC nanowires (SiCNWs) were incorporated into the epoxy matrix to characterize the morphology effect on their electromagnetic wave absorption performance. The ultra-long SiCNWs with lengths of hundreds of micrometers were fabricated by chemical vapor deposition technique at 1250 °C, and have diameters of 10-60 nm with uniform morphologies. The microwave absorption performance of SiCNW/epoxy resin composites was investigated in the range of 8-18 GHz. Significant absorbing properties were discovered in the composites at frequencies of 8-12.4 GHz, comparing with a control sample. The slightest reflection loss (RL) value of -0.5 dB was obtained at 15 GHz at a very small SiCNWs concentration of 0.05 wt%. The significant absorbing properties of the uniform ultra-long SiCNWs at low frequencies can be mainly attributed to homogeneous small diameters to reduce the electromagnetic wave reflectance, high density interfacial polarization, complex conductive network structure and quantum effect.