The　composition　and　microstructures　of　the　Al2O3-SiO2　system　coatings　fabricated　by　chemical　vapor　deposition　using　AlCl3-SiCl4-H-2-CO2　were　investigated.　The　results　show　that　completely　compositional　homogenization　between　silica　and　alumina　does　not　occur　under　CVD　conditions.　The　products　deposited　all　were　the　transition　Al2O3　attached　amorphous　SiO2.　The　size　of　the　Al2O3-SiO2　particles　declined　with　CVD　temperature　increasing　in　the　range　of　550degreesC　to　850degreesC.　Dense　and　crystalline　3Al(2)O(3)(.)SiO(2)-alpha-Al2O3-iota-Al2O3-SiO2　coating　was　obtained　by　CVD　at　1050degreesC.