Amorphous and polycrystalline Ba0.9Sr0.3TiO3 thin films were deposited on Si(100) and fused quartz substrates by a modified sol-gel technique. X-Ray diffraction analysis clearly shows the formation of a perovskite structure at approximately 700 degreesC. An amorphous nature was found for films annealed below 600 degreesC, and their inferior crystallinity suggested the formation of an incomplete perovskite phase. The dominant surface feature was a cone-like protrusion observed by atomic force microscopy. The average grain size was approximately 70 nm for the film annealed at 700 degreesC. The optical constants were determined from spectrophotometric measurements of the transmittance in the wavelength regime of 200-900 nm at room temperature, The effects of the annealing temperature on the optical and structural properties of the films were investigated.