Submicro-composites of core-shell C/Co were synthesized by a two step process of liquid synthesis and heat treatment with C as core- and Co as shell-material, and then their microwave absorption properties were investigated. Results show that the heat treatment process can enhance the crystallinity of the prepared C/Co-composites and alter their morphology, i.e. transforming from a core/shell structure with snowflak like shell to a core/shell structure with enclosed shell. Meanwhile,their saturation magnetization of increases while coercivity decreases. Finally a mixture of the prepared C/Co-composite with paraffin (50%, mass fraction) show excellent microwave absorption property i.e. a layer of such mixture of 2.5 mm in thickness exhibits a minimum reflection loss (RL) of -23 dB at 11 GHz ,and an effective bandwidth (RL<-10 dB) of 3 GHz. With the increase of layer thickness, the absorption peak shifts gradually to low frequencies and multiple-absorption peaks emerge. The excellent microwave absorption properties may be attributed to the better impedance matching, dielectric loss and quarter-wavelength interference cancellation etc..