A highly refractive and transparent poly(phenylene thioether) containing a triazine unit has been developed. The polymer was prepared by a polycondensation procedure from 4,4'-thiobis(benzenethiol) and 2,4-dichloro-6-methylthio-1,3,5-triazine and showed good thermal stabilities such as a relatively high glass transition temperature at 116 degrees C and a 5% weight-loss temperature (T-5%) at 367 degrees C. The optical transmittance of the polymer at 400 nm is higher than 80%. The triazine unit with sulfur atoms provides the polymer with a high refractive index of 1.7492 at 633 nm.