Abstract Natural rubber/epoxidized natural rubber (NR/ENR) composites with 30 wt% conductive carbon black (CCB) were prepared by tow-roll mechanical mixing. Influences of NR/ENR blend ratios on the morphology and electromagnetic properties of CCB/NR/ENR composites were studied. Thermodynamic and morphological analysis indicated that co-continuous NR/ENR blend favored the formation of CCB network, providing the composites with superior electromagnetic properties. Electrical conductivity, dielectric loss and reflection loss over C-band (8–12 GHz) of CCB/NE/ENR composite were found to be a function of NR/ENR ratio, and reached the optimum value of 0.34 S/m, 0.31 and −23.58 dB when NR/ENR was 70/30 (wt./wt.), respectively. A morphology-promoted electromagnetic wave attenuation mechanism was proposed.