Nanocrystalline titanium and indium oxides and TiO2-In2O3 composites have been prepared by sol-gel technique using concentrated hydrous titanium dioxide and indium hydroxide sols. Structure, optical, and photoelectrochemical properties of the composites with different molar ratios of TiO2 to In2O3 have been studied. The binary oxide films and xerogels annealed at temperatures from 200 to 700 degreesC have a nanocrystalline structure without the chemical interaction between the oxides. However, there is a strong mutual influence of the components of the binary oxide systems, during their annealing which manifests itself in thermogravimetry and differential scanning calorimetry measurements and in a marked effect on the oxide crystallite size. Highly transparent TiO2-In2O3 films fabricated by spin-coating technique exhibit extreme dependencies of the various optical and photoelectrochemical properties on the film composition. The band gap edge of the composite films is blue-shifted, as compared with that of single-component films. Possible causes of these effects have been discussed, The conductivity of TiO2-In2O3 films changes by 6 orders of magnitude in the range of compositions near the calculated value for percolation threshold associated with the formation of 3D infinite clusters of interconnected In2O3 nanoparticles.