Developing lightweight and highly efficient electromagnetic wave (EMW) absorbing materials is crucial but challenging for anti-electromagnetic irradiation and interference. Herein, we used multiwalled carbon nanotubes (MWCNTs) as templates for growth of Co-based zeolitic imidazolate frameworks (ZIFs) and obtained a Co–C/MWCNTs composite by postpyrolysis. The MWCNTs interconnected the ZIF-derived Co–C porous particles, constructing a conductive network for electron hopping and migration. Moreover, the Co–C/MWCNTs composite was aligned in paraffin matrix under an external magnetic field, which led to a stretch of the MWCNTs along the magnetic field direction. Due to the anisotropic permittivity of MWCNTs, the magnetic alignment considerably increased the dielectric loss of the Co–C/MWCNTs composite. Benefiting from the conductive network, the orientation-enhanced dielectric loss, and the synergistic effect between magnetic and dielectric components, the magnetically aligned Co–C/MWCNTs composite exhibited extremely strong EMW absorption, with a minimum reflection loss (RL) of −48.9 dB at a filler loading as low as 15 wt %. The specific RL value (RL/filler loading) of the composite was superior to that of the previous MOF-derived composite absorbers. It is expected that the proposed strategy can be extended to the fabrication of other lightweight and high-performance EMW-absorbing materials.