Lithium　cobalt　oxide　was　synthesized　by　sol-gel　with　citric　acid.　The　crystallization　process　of　LiCoO2　gel　precursor　was　studied　by　TG-DSC,　and　then　it　was　calcined　from　400　to　800C.　The　crystal　structures　of　LiCoO2　powders　formed　at　different　temperatures　were　analyzed　through　X-ray　diffraction,　Infrared　spectrum,　Raman　spectrum　and　transmission　electron　microscope.　The　results　show　that　the　mean　grain　sizes　of　LiCoO2　powders　are　about　20-40　nm,　and　increase　with　calcinating　temperature　changing　from　400　to　700C,　while　decrease　at　800C.　The　structure　changed　from　modified　spinel　to　layered-rock-salt　with　the　calcinating　temperature　from　400　to　800C.　In　the　modified　spinel　structure,　Co2+　ions　reside　at　the　tetrahedral　sites　and　Co3+　ions　reside　at　the　octahedral　sites.　However,　in　the　layered-rock-salt　structure,　just　only　Co3+　ions　reside　at　the　octahedral　sites.