Graphene oxide (GO) is one of the most important derivatives of graphene. GO nanosheets/epoxy composites were prepared by oxidization and ultrasonic dispersion. The structure and morphology of GO nanosheets were characterized by XRD, Raman spectrum, FTIR and TEM. The effects of GO nanosheet content on the thermal stability, mechanical property and dielectric property of GO nanosheets/epoxy composites were discussed. The results show that the thermal stability of GO nanosheets/epoxy composites is improved by adding GO nanosheets. The impact strength and bending strength first increase and then decrease with increasing GO nanosheets loading. Dielectric constant and dielectric loss first decrease and then increase. The thermal decomposition temperature with 5% mass loss is improved from 400.2 ℃ for the pure epoxy to 424.5 ℃ for the GO nanosheets/epoxy composites with 0.3wt% GO nanosheets loading. Furthermore, the impact strength and bending strength with 0.2wt% and 0.3wt% GO nanosheets loading reach the maximum respectively, increasing from 10.5 kJ/m
2 for the pure epoxy to 19.7 kJ/m
2 and from 80.5 MPa to 104.0 MPa.