The preparation of SiO2-TiO2 thin films by the sol-gel method using silicic acid and titanium tetrachloride as starting materials was studied. The homogeneous sols were obtained by the condensation reaction of silicic acid with titanium tetrachloride in methanol-tetrahydrofuran. The dip-coating of slide glasses and silicon wafers followed by heat treatment gave oxide thin films of 88-93% transmittance, 3000-4500 angstrom thickness, and 1.45-1.80 refractive index, depending on heat-treatment temperature and TiO2 content. FT-IR measurement showed that the Si-O-Ti bond is formed even in the sol and films. The variations of film thickness and refractive index on transformation from the gels into the oxides were found to be quite low.