A series of oriented liquid-crystalline epoxy thin films were prepared by the in situ polymerization of a liquid-crystalline diepoxide, 1,4-phenylene bis[4-(2,3-epoxypropoxy)benzoate], with an aromatic diamine, 4,4'-diaminobiphenyl, in a 7.0-T magnetic field. The birefringent measurements of the oriented films were made from 543.5 to 830 nm. In this range, the values of birefringence (Deltan) range from 0.155 to 0.130. When they are extrapolated to the microwave region, Deltan = 0.105. The dichroism of a guest azo dye, 4-(4-nitrophenylazo)-3-hexyloxyaniline, in the oriented thin films was examined in the visible region. From the results, the order parameter of the polymer was calculated to 0.65 by extrapolating the concentration of the guest azo dye to zero. The guest azo dye compound does not affect the birefringence.