Abstract: The graphene oxide was reduced by hydrazine hydrate to attain two kinds of reduced graphene oxide (rGO) with different oxygen contents. The prepreg was prepared from carbon fiber (CF) and bismaleimide (BMI) resin by wet impregnating process, then the rGO-CF/BMI composite unidirectional laminates were manufactured by hot pressing process. The relationship between reduced degree and content of rGO and mechanical properties, glass transition temperature and electromagnetic properties of composites was studied. The results show that the reduced degree of rGO2 which was attained under the higher temperature is larger than that of rGO1 which was attained under the lower temperature, the dispersion of rGO2 is poorer than rGO1 in resin. The interlaminar shear strength of rGO1-CF/BMI and rGO2-CF/BMI composites will both be enhanced about 14% compared to CF/BMI composites when the mass fraction of rGO1 and rGO2 is 0.1% and 0.05% respectively, however, the flexural properties and glass transition temperature are basically unchanged. The dielectric properties of rGO2-CF/BMI composites are superior to those of rGO1-CF/BMI composites. When the mass fraction of rGO2 is 0.1%, the real part dielectric constants of rGO2-CF/BMI composites will increase by over 6 times than those of CF/BMI composites, as well as the dielectric losses will increase by over 3 times at the frequency range of 12.4-18.0 GHz. Moreover, the magnetic properties of rGO1-CF/BMI and rGO2-CF/BMI composites are pretty weak, thus the interaction between the composites and electromagnetic wave is mainly reflection, rather than absorption.