Lanthanum-substituted bismuth titanate (BLT) thin films were deposited on fused silica substrates by chemical solution deposition method. The crystallinity of BLT was examined by X-ray diffraction. The optical properties of the BLT thin films have been investigated by optical transmission spectra and spectroscopic ellipsometry. The refractive index n and the extinction coefficient k of the BLT thin films were obtained. The birenfrigent shift as a function of applied voltage of BLT thin films on fused silica was measured. The BLT samples showed a quadratic response and quadratic electro-optic coefficient R=1.48×10-18 (m/V)2 was gotten at He-Ne laser632.8 nm.