A new thermoplastic, poly(thioether sulfone) (PES), with the highest refractive index and high Abbe's number among thermoplastics has been developed by the simultaneous introduction of sulfide, sulfone, and alicyclic units in the polymer chains. The PES with a high molecular weight was prepared by the Michael polyaddition of 2,5-disulfanyl-1,4-dithiane with divinyl sulfone. The flexible, tough, transparent, and amorphous PES film was obtained and showed a good thermal stability with 5% weight loss temperature of 275 degrees C in nitrogen and the glass transition temperature of 152 degrees C. The PES exhibited the highest refractive index of 1.686 and the Abbe's number of 48.6 among thermoplastics.