Undoped, 5%, and 10% lanthanum doped lithium tantalate thin films were annealed at 550 • C temperature for 12.5 hours and their properties were characterized. The results showed that the dopant addition affects the crystal formation of LiTaO 3 , especially the 10% La 2 O 5 dopant, where the lattice of a = 5.11 Å, c = 13.30 Å, and its crystal was hexagonal. The observed functional groups were O-H, N-H, C = C, Li-O, Ta-O. The higher La 2 O 5 dopant concentration leads to the higher absorption of Ta-O and Li-O, the lower the energy gap, the higher the refractive index, and the smaller the particle size of thin films.