CoO　nanostructures　with　tunable　morphology　and　size　have　been　prepared　via　a　simple　one-pot　solvothermal　synthesis.　The　as-prepared　nanoparticles　were　fully　characterized　using　X-ray　diffraction　(XRD),　transmission　electron　microscopy　(TEM),　field-emission　scanning　electron　microscope　(FESEM),　etc.　The　morphology　and　size　of　the　product　can　be　easily　controlled　by　adjusting　the　raw　materials　added.　Reaction　time　and　the　solvent　ratio　also　play　important　roles　in　the　synthesis　of　octahedral　nanostructures.　The　magnetic　property　of　the　as-prepared　samples　was　also　investigated.