Highly refractive and transparent polyimides (PIs) containing a 3,4,8,9-tetrahydro-2,5,7,10-tetrathiaanthracene moiety in their main chains have been developed. These Pis were prepared from several dianhydrides such as 4,4'-[p-thiobis(phenylsulfanyl)]diphthalic anhydride (ODPA), 4,4'-[(9H-fluorene-9-ylidene)bis(p-phenylsulfinyl)]diphthalic anhydride (FPSP), 4,4'-oxidiphthalic anhydride (ODPA), and a new sulfur-containing aromatic diamine, 1,6-bis(p-aminophenylsulfanyl)-3,4,8,9-tetrahydro-2,5,7,10-tetrathiaanth racene (BTTA), by a two-step polycondensation procedure. The Pis exhibit good thermal and optical properties such as glass transition temperatures higher than 213 degrees C, thermal decomposition temperatures (T-10%) in the range of 390-443 degrees C, and optical transparency higher than 80% at 500 nm for a thickness of ca. 10 mu m. Because of the very high sulfur content (28.4%) in the polymer main chain, the PI derived from BTTA and 3SDEA exhibits the highest refractive index, i.e., 1.769 at 633 am.