Silica-titania and silica-alumina aerogels were prepared by the two-step hydrolysis of metal alkoxides, the sol-gel polymerization and the supercritical drying with carbon dioxide. As a result of characterization by nitrogen adsorption, the aerogels were mesoporous materials with high surface areas and had few micropores. The experimental results suggested that the surface area, the mesopore volume, and the pore radius of the aerogel depended on the titanium (Ti) or aluminum (Al) content. Adsorption isotherms of ethane, ethylene, propane, and propylene were measured on the aerogels prepared. It was found that the adsorption capacities for these hydrocarbons were changed by mixing Ti or Al to the silica aerogel. In the ethane-ethylene or propane-propylene system, the adsorption selectivity of ethylene or propylene on the silica-titania aerogel was lower than that on the silica aerogel. On the other hand, the selectivity on the silica-alumina aerogel was higher than that on the silica aerogel. Hence, the silica-alumina aerogel was useful for separating ethylene from ethane or propylene from propane.