Highly refractive and transparent polyamides containing thiadiazole units have been developed. These polymers were prepared by a polycondensation reaction of 4

4′-(1

3

4-thiadiazole-2

5-thio) bis(methylene) dibenzoyl chloride (TDTBM-DC) and diamine which contained thioether (—S—) and sulfone units. They showed good thermal stabilities such as a relatively high glass transition temperature of 206−233 ℃ and a 5% weight-loss temperature (

T

5%

) of 376−395 ℃. The optical transmittance of the polymer at 450 nm is higher than 83%. The heterocycle units and plural —S— linkages provide the polymer with a high refractive index of 1.716−1.725 at 633 nm and a low birefringence of 0.003−0.004. Also they showed improved solubility in polar aprotic solvents and could form moderate strength films with tensile strength of 72.8−83.1 MPa and storage modulus of 1.0−1.8 GPa (at 200 ℃).