A series of copolyimides were prepared from two alicyclic dianhydrides having the common molecular formula C10H8O6, rel-[1S,5R,6R]-3-oxabicyclo[3.2.1]octane-2,4-dione-6-spiro-3'-(tetrahydr ofuran-2',-5'dione) (DAn) and c-3-carboxymethyl-r-1,c-2,c-4-cyclopentanetricarboxylic acid 1,4:2,3-dianhydride (TCAAH), with p-phenylenediamine (PPD) by a conventional two-step procedure. With increasing DAn fractions in the backbones, the copolyimides showed better film formability, enhanced solubility, increased glass transition temperatures and birefringences, and decreased average refractive indices. The unsymmetric spiroalicyclic structure of DAn might be responsible for these results. Films of copolyimides obtained by both thermal and chemical imidization were fully transparent and were colorless or pale yellow depending on the film thickness.