Mixed sol of TiO2-B2O3 was prepared from titanium sec-butoxide and boric acid. This sol could be aged into a clear gel, or dip coated into a transparent film. X-ray diffraction studies on the dried gel show that the transformation from anatase to rutile structure began below 500-degrees-C. This temperature is less than the case of pure TiO2. Based on Fourier transform infrared spectra, it is suggested that, after annealing, most boron is in orthoborate groups, the amount of which increases with increasing annealing temperature. The addition of B2O3 also changed the refractive index of the film produced by dip coating, and increased its transmittance in the wavelength range below 550 nm. In addition, it increased the alkaline and acid resistance of the film. Unlike the sol prepared from boron alkoxide, the sol prepared from boric acid was less affected by the atmospheric humidity during the coating process.