Nanoparticles　of　cerium　oxide　were　prepared　by　common　precipitation　method　using　cerium　nitrate　solution　and　ammonia　reagent.　Cerium　oxide　particles　with　different　morphologies　were　synthesized　through　adjusting　pH　values　of　the　solution.　TEM　and　BET　results　showed　that　spherical　crystal　was　gained　in　acid　solution,　with　the　specific　surface　of　148.1944　m(2.)g(-1).　The　cerium　oxide　appeared　in　the　form　of　spherical　and　rod-like　grains　under　neutral　condition,　and　the　specific　surface　changed　to　114.7975　m(2.)g(-1).　Moreover,　in　alkaline　solution,　cerium　oxide　powders　were　exhibited　in　rod-like　form　with　the　specific　surface　of　106.2465　m(2.)g(-1).　Precipitation　formation　mechanism　of　different　morphologies　was　also　discussed,　which　followed　decomposition　precipitation　mechanism　and　topology　reaction　mechanism　in　acid　and　alkaline　solution,　respectively.