A　CeO2-ZrO2-Al2O3　composite　oxide　(CZA)　and　a　CeO2-ZrO2　composite　oxide　(CZ)　were　prepared　by　the　co-precipitation　method.　The　samples　were　thermally　aged　in　a　flowing　air　atmosphere　and　in　10%　H-2/Ar　flow.　The　structure　and　performance　of　the　composite　oxides　were　studied　by　X-ray　diffraction　(XRD),　oxygen　storage　capacity　(OSC)　measurements,　and　H-2　temperature-programmed　reduction　(H-2-TPR).　The　results　show　that　a　CeAlO3　phase　was　formed　after　CZA　was　reductively　aged　at　950　degrees　C　and　an　increase　in　temperature　benefited　the　formation　of　CeAlO3.　The　OSC　of　CZA　increased　with　an　increase　in　the　reductive　treatment　temperature　and　it　was　1270.3　mu　mol.g(-1)　when　the　temperature　reached　900　degrees　C.　However,　the　OSC　decreased　with　an　increase　in　the　temperature.　After　CZA　was　reduced　at　1100　degrees　C　the　OSC　was　only　23.2　mu　mol.g(-1).　We　found　that　the　OSC　and　the　reducibility　of　the　material　were　remarkably　influenced　by　the　formation　of　a　CeAlO3　phase　after　CZA　was　reductively　aged.