In Greek mythology, Mestra (Ancient Greek: Μήστρα, Mēstra) was a daughter of Erysichthon of Thessaly. She had the ability to change her shape at will, a gift of her lover Poseidon according to Ovid.
Her father exploited this gift in order to sate the insatiable hunger with which he had been cursed by Demeter for violating a grove sacred to the goddess. Erysichthon would repeatedly sell Mestra to suitors for the bride prices they would pay, only to have the girl return home to her father in the form of various animals.
According to Ovid, Mestra married the thief Autolycus.