Novel poly(phenylene thioether)s containing pyrimidine rings and fluorene units in the main chain have been developed as promising candidates for thermoplastic lenses which are used for compensating chromatic aberration. The obtained polymers showed a good thermal stability (i.e., 5% weight-loss temperature over 320 °C) and relatively high glass transition temperatures in the range of 132–201 °C. The cutoff wavelengths of the polymer thin films are shorter than 320 nm, and a transmittance higher than 90% was observed over 380 nm. The polymer containing a fluorene unit with the highest sulfur content exhibited the highest refractive index of 1.678 and the low birefringence of 0.004 at 633 nm.