In Greek mythology, Polymestor was a King of Thrace.

Polydorus, King Priam's youngest son, was sent with gifts of jewelry and gold to the court of King Polymestor to keep him safe during the Trojan War. The fighting was getting vicious and Priam was frightened for the child's safety. After Troy fell, Polymestor threw Polydorus to his death to take the treasure for himself. Hecuba, Polydorus' mother, eventually avenged her son.