The　hydrophobic　nanocomposites　of　reduced　graphene　oxide　(RGO)　and　Fe3O4　(RGO/Fe3O4)　were　prepared　by　a　one-pot　process　through　co-precipitation　under　alkaline　conditions.　The　microwave　absorption　performance　of　the　RGO/Fe3O4　nanocomposites　was　analyzed　according　to　their　electromagnetic　parameters.　The　results　showed　that　the　RGO/Fe3O4　nanocomposites　displayed　better　absorbing　performance　than　the　pristine　Fe3O4　nanoparticles,　owing　to　the　synergistic　effect　of　Fe3O4　and　RGO.　The　maximum　reflection　loss　(RL)　of　the　RGO/Fe3O4　nanocomposites　with　a　thickness　of　2　mm　reached　-45.7　dB　at　13.3　GHz,　and　the　bandwidth　(RL　＜　-10　dB)　ranged　from　11.5　to　16.5　GHz.　However,　the　maximum　RL　of　the　Fe3O4　nanoparticles　with　a　thickness　of　5　mm　only　reached　-5.3　dB　at　5.7　GHz.　The　RGO/Fe3O4　nanocomposites　have　a　great　potential　application　in　high-performance　electromagnetic　microwave　absorbing.