To evaluate the microwave absorption properties of the graphene oxide (GO) sheets capsulated on carbonyl iron particles (CIP), we synthesized the GO capsulated on carbonyl iron particles (GOCIPs) by a simple wet stirring process. Complex permittivity were increased with the increment of mass ratio of GO in GOCIPs from 0.5 to 2 wt % while the complex permeability values were not changed. The maximum reflection loss (RLmax) and frequency bandwidth at -10 dB (BW@-10 dB) of the 1.9 mm thick-GOCIP composite with 2.0 wt% of GO in GOCIPs exhibited about -56.4 dB @10.8 GHz and 5.1 GHz. The RLmax frequency shifted to lower frequency with the increment of absorber thickness from 1 mm to 3 mm. BW@-10 dB decreased with the increment of absorber thickness.