Bi3.25La0.75Ti3O12(BiLT) thin films with different thickness were successfully deposited onto fused quartz by chemical solution deposition. X-ray diffraction analysis shows that BiLT thin films are polycrystalline with (0 0 2)-preferred orientation. The dispersion of refractive indices of the BiLT thin films was investigated by the optical transmittance spectrum. The optical band gap energy was estimated from the graph of (hvalpha)(2) versus hv. The results show that the refractive index and band-gap energy of the BiLT thin films decrease with the films thickness. (C) 2004 Elsevier Ltd. All rights reserved.