TiO2-SiO2 homogeneous sol was prepared by means of complexing titanium iso-propoxide with acetylacetone. Crack-free, monolithic binary TiO2-SiO2 aerogels were obtained by evacuating the solvent under the pressure of 2,200 psi at 28$0^{circ}C$, which was determined as a supercritical condition. The microstructure of the binary aerogels was observed to be finer and more homogeneous as the Ti content decreased. The microstructure was related to the optical transition of aerogels from opaque to transluscent.