The　Fe3O4　magnetic　nano-particles　prepared　by　the　titration　hydrolyzation　method　were　studied　with　X-ray　diffration(XRD),　UV-Vis　diffusive　reflectance　spectrum(DRS),　Magnetoresistance　measurement　and　digital　bridge　LCR.　The　results　show　that　the　Pe(3)O(4)　magnetic　particles　have　strong　absorptions　in　the　rang　from　250nm　to　3000mn;　the　average　diameter　of　the　Fe3O4　nano-particles　is　about　18nm.　The　Fe3O4　granular　film　has　obvious　negative　magnetoresistivity　effect　and　humidity　sensitive　character.　The　impedance　of　the　Fe3O4　nano-particles　decreases　with　increasing　magnetic　induction　and　humidity　respectively.