In　the　water/oil　microemulsion　system　of　cetyl　trim　ethylamine　bromide+butanol/cyclohexane/water　solution,　the　microemulsion　area　was　measured　and　cerium　oxide　nanoparticles　were　prepared　according　to　the　principle　by　liquid-liquid　two　phase　method.　The　samples　were　analyzed　by　means　of　transmission　electron　microscope,　X-ray　diffraction,　thermogravimetric-differential　scanning　calorimetry,　infrared　spectroscopy.　The　morphology,　phase　and　components　were　investigated.　The　results　show　clearly　that　nanometer　cerium　oxide　could　be　prepared　in　the　measured　area　of　microemulsion　and　it　is　an　effective　way　to　gain　well　dispersed　and　uniformly　distributed　nanometer　cerium　oxide　grains　with　the　size　of　about　3　nm.