Absorbents with lightweight, low filler loading and broadband absorption are highly desired in electromagnetic wave absorbing field. Herein, the carbon black/reduced graphene oxide (CB/RGO) composite materials were fabricated via a facile synthetic method. The composite absorbents demonstrate an excellent microwave absorption performance. With the low filler loading of 7 wt%, the maximum absorption is as strong as 47.5 dB and the effective absorption bandwidth (reflection loss < -10 dB) reaches 5.92 GHz covering 37% of the entire measured bandwidth at only 2.2 mm thickness. Compared with the CB particles, CB/RGO composites possess higher absorption intensity and broader effective absorption bandwidth. This work provides a feasible approach for the design and synthesis of composite absorbents with lightweight and high-performance absorption.