Al 2 O 3 -TiO 2 composite oxide nanocrystals with different Al 2 O 3 /TiO 2 ratios (1/4, 2/3, 3/2, and 4/1) were prepared by the poly(ethylene glycol) (PEG) sol-gel method. The preparation process was monitored by thermogravimetric analysis and differential scanning calorimetry (TGA-DSC). Nanocrystal particles of these composite oxides obtained at various heat-treating temperatures (400-1100°C) were characterized in terms of morphology, size, specific surface area, composition, and structure by transmission electron microscopy (TEM), BET specific surface area analysis, and X-ray powder diffractometry (XRD). Nanoparticles of Al 2 O 3 -TiO 2 with grain sizes in the range 1-150 nm and specific surface areas of 4.3-136 m 2 /g could be obtained under different conditions. The morphology of the particles changed from spherical to cubic with increasing heat-treatment temperature. Anatase was stabilized in these composite nanomaterials and the mechanism was discussed. The change of the particles specific surface areas with increase of the Al 2 O 3 /TiO 2 ratio was researched. The Al 2 O 3 -TiO 2 composite oxide nanocrystals could catalyze the polymerization of maleic anhydride and may provide a route to obtain a product without rings at the end groups.