A highly refractive and transparent aromatic polyimide (PI) containing a selenophene unit has been developed. The PI was prepared by a two-step polycondensation procedure from 2,5-bis(4-aminophenylenesulfanyl)selenophene (APSP) and 4,4'-[p-thiobis(phenylenesulfonyl)]diphthalic anhydride (3SDEA), and shows high thermal stabilities, such as a relatively high-glass transition temperature of 189 degrees C and 5% weight loss temperature (T-5%) of 418 degrees C. The optical transmittance of the PI film at 450 nm is higher than 50%. The selenophene unit provides the PI with a refractive index of 1.7594, which is higher than corresponding PIs containing a thiophene or a phenyl unit because of the high polarizability per unit volume of the selenium atom. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4428-4434, 2009