Fully imidized and solvent soluble polyimide films with a polyalicyclic structure were prepared from bicyclo[2.2.2]octane-2, 3, 5, 6-tetracarboxylic 2, 3:5, 6-dianhydrides and aromatic diamines. The optical properties such as optical transparency and refractive indices have been evaluated. These films were entirely colorless, and the normalized transparencies in the visible region were over 86%. The films remained colorless and transparent up to 300°C when heated in air, and 400°C in N₂. The polyimides had an average refractive index range of 1.599 to 1.617. The birefringencies of the BAB-based polyimides were nearly zero.