Alumina/silica microspheres were prepared by sol-gel process in oil-in-water emulsion with aluminum sec-butoxide as aluminum source and tetraethoxysilane as silicon source, crystallization was achieved by heat treatment at 1000 oC. The effect of addition of tetraethoxysilane and heat treatment on the crystalline structure and microstructure of the microspheres were studied via scanning electron microscopy, X-ray diffraction and thermogravimertic/diifrental thermal analysis analysis. The results showed that increasing addition of tetraethoxysilane inhibited the gelation of the disperse phase in emulsion, which induced the conglutination of the disperse phase. After heat-treated at 100 oC, the mulite phase in the alumina/silica microspheres was generated and the resulting grain size was12 nm.