The surfaces of TiO2 nanocrystals were modified with amorphous aluminum-oxide layers using a surface sol-gel process to control the interaction between supports and metal particles. Ultrastable Au nanocatalysts were prepared by the deposition of Au nanoparticles on the surface-modified TiO2 nanocrystals using a deposition-precipitation (DP) method. The TEM analysis showed that the Au nanoparticles on the surface-modified nanocrystal supports were highly stable with a sinter-resistant capability during high-temperature calcination. The HRTEM analysis revealed that the surface of the TiO2 nanocrystals was covered by an amorphous aluminum-oxide layer and the Au nanoparticles were primarily anchored to this amorphous layer. This amorphous aluminum-oxide layer played an extremely important role in the stabilization of the supported Au nanoparticles without affecting catalytic activities. The surface modification of nanocrystal supports highlights new opportunities in tailoring the stability and activity of supported nanocatalyst systems.