Abstract Core-shell structured silicon carbide (SiC)/epoxy (EP) composites exhibit superior non-linear DC conductivity. However, the high voltage alternative current (HVAC) dielectric properties of the composites are rarely reported. In this paper, the time-domain measurement was employed to obtain the basic dielectric characteristics, AC conductivity, and relative permittivity of the SiC/EP and SiC@Al2O3/EP composites under less than the breakdown strength of the SiC/EP (i.e., the amplitude of 1-5 kV/mm). In addition, in the high AC electric field (i.e., the amplitude of 6-20 kV/mm), the non-linear AC dielectric properties of the SiC@Al2O3/EP composite are also investigated. The experimental results suggest that the SiC@Al2O3/EP composite shows more obvious non-linear AC dielectric properties than the SiC/EP composite. In the high AC electric field, the AC conductivity of the SiC@Al2O3/EP composite presents the relaxation phenomenon, which is attributed to the excitation field and its derivative. This work lays a foundation for further research on the AC steady-state and transient dielectric properties of the field grading materials, which are widely used to homogenize the nonuniform electric field distribution in many electrical and electronic equipment.