Abstract: Al₂O₃ nanosheets were successfully synthesized by hydrothermal process.After modified with coupling agent, Al₂O₃ nanosheets/epoxy composites with different contents of Al₂O₃ nanosheets were prepared by solution mixing.The effects of Al₂O₃ nanosheet content on the dielectric and thermal properties of Al₂O₃ nanosheets/epoxy composites were discussed.The fracture morphology of composites was characterized by SEM.The results show that Al₂O₃ nanosheets uniformly disperse in epoxy matrix.With the increase of Al₂O₃ nanosheet content, the initial thermal decomposition temperature and the dielectric strength of Al₂O₃ nanosheets/epoxy composites increase.Dielectric strength of composites is 29.58 kV/mm with 7wt% Al₂O₃ adding, which is increased by 30% than that of the pure epoxy.Dielectric constant (3.8-4.5) and dielectric loss (0.015) of Al₂O₃ nanosheets/epoxy composites increase slightly than pure epoxy's, but the dielectric properties still remain at a good level.