Ultrafine alumina-silica powders with varying composition gradients within the particles have been produced by chemical vapor synthesis in a hot-wall reactor using the precursors tetraethoxysilane (TEOS) and aluminiumtrisecbutylate (ASB). The surface chemistry at the particle/liquid interface in aqueous dispersions can be adjusted by varying the process parameters. The powders have been characterized by nitrogen adsorption, X-ray diffraction (XRD), transmission electron microscopy (TEM) with local energy dispersive X-ray (EDX) analysis, X-ray fluorescence (XRF) analysis, and electrophoretic mobility measurements.