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Si 3 N 4 ceramics modified with SiC nanofibers were prepared by gel casting aiming to enhance the dielectric and microwave absorption properties at temperatures ranging from 25 °C to 800 °C within X-band (8.2–12.4 GHz). The results indicate that the complex permittivity and dielectric loss are significantly increased with increased weight fraction of SiC nanofibers in the Si 3 N 4 ceramics. Meanwhile, both complex permittivity and dielectric loss of SiC nanofibers modified Si 3 N 4 ceramics are obviously temperature-dependent, and increase with the higher test temperatures. Increased charges mobility along conducting paths made of self-interconnected SiC nanofibers together with multi-scale net-shaped structure composed of SiC nanofibers, Si 3 N 4 grains and micro-pores are the main reason for these enhancements in dielectric properties. Moreover, the calculated microwave absorption demonstrates that much enhanced microwave attenuation abilities can be achieved in the SiC nanofibers modified Si 3 N 4 ceramics, and temperature has positive effects on the microwave absorption performance. The SiC nanofibers modified Si 3 N 4 ceramics will be promising candidates as microwave absorbing materials for high-temperature applications. [ABSTRACT FROM AUTHOR]