In Greek mythology, Absyrtus (Ancient Greek: Ἄψυρτος) or Apsyrtus was a Colchian prince and the younger brother of Medea. He was involved in Jason's escape with the golden fleece from Colchis.

The Absyrtides were named after him.

Absyrtus was the son of Aeëtes, king of Colchis and a brother of Medea and Chalciope. His mother is variously given: Hyginus calls her Ipsia, Hesiod and the Bibliotheca call her Idyia, Apollonius calls her Asterodeia, a Caucasian Oceanid and others Hecate, the Nereid Neaera or Eurylyte.

A tradition followed by Pacuvius, Justin, and Diodorus provided Aegialeus as the name of the son of Aeëtes who was murdered by Medea. Absyrtus was also called Phaethon by the sons of the Colchians because he outshone all the youths.

As a descendant of Helios, Apsyrtus grew into a radiant young man and lived in his own palace, next to the loftiest building where his father, the queen and his other sisters dwelt. This can be explained by the fact that Apsyrtus was born to a Caucasian nymph, Asterodeia, to Aeetes before he made Eidyia, the youngest daughter of Tethys and Oceanus, his wedded wife. Because his grandfather, Helios, had once betrayed Ares to the other gods for being the lover of the beautiful Aphrodite, the love-goddess was extremely hostile to the descendants of Helios and none of them would experience a happy love life.

Later on, a civil war in Colchis occurred because the brother of Aeëtes, Perses, came with a Scythian army to the country in order to unseat the king out off his throne. Aeetes was aided by the Argonauts because he vowed to give the Golden Fleece to Jason in return of the favor for the incoming fight.

During the battle, Apsyrtus went to the front line and wore a beautiful golden armor. He drove the golden cart of his grandfather Helios while his golden shield reflected the rays of the sun. He had a quivering spear and a threatening, gleaming helm that no one of the common people could gaze at without getting pain in their eyes. When he pursued his opponents in battle, they fled from fear and he ran over them with his horses. Groaning, the trampled warriors remained in the dust and wondered anxiously what had happened to them. Finally, Aeetes with the help of the Minyans won the war and managed to chase away his brother.

When Medea fled with Jason, she took her brother Absyrtus with her, and when she was nearly overtaken by her father, she murdered her brother, cut his body into pieces and strewed them on the road, so that her father might thus be delayed by gathering the limbs of his child. Tomi, the place where this occurred, was believed to have derived its name from temno (τέμνω, "cut").