Demetrius II Aetolicus (Greek: Δημήτριος ὁ Αἰτωλικός) son of Antigonus Gonatas and Phila, reigned as king of Macedonia from the winter of 239 to 229 BC. He belonged to the Antigonid dynasty and was born in 275 BC. There is a possibility that his father had already elevated to him to position of power equal to his own before his death. If this had occurred it would be dated at 256 or 257 BC.
He had already during his father's lifetime distinguished himself by defeating Alexander II of Epirus at Derdia and so saving Macedonia (c. 260 BC). On his accession he had to face a coalition of enemies which included the two great leagues. Usually rivals, the Aetolian League and Achaean League, now became allies against the Macedonian power. He succeeded in dealing this coalition severe blows, wresting Boeotia from their alliance. The revolution in Epirus, which substituted a republican league for the monarchy, gravely weakened his position.
During his reign his kingdom extended to Euboea, Magnesia, Thessaly and its environs, excluding Dolopia and possibly Peparethos and Phthiotic Achaia.
In 236 BC he invaded Boetia, making the Boetians submit immediately.
In 234 BC due to the Federal Republic replacing the monarchy in Epirus led to the events of 231 BC, Demetrius hired Agron for military aid against advancing Aetolians. His kingdom was not threatened by the Illyrian Ardiaei ruled by Agron despite them having gathered the greatest force in their history (around 231 BC), but Epirus needed some sort of force to deter them.
Demetrius in the end of his reign defended his domain from the tribal peoples of the north. A battle with the Dardanians turned out disastrously, and he died shortly afterwards, leaving Philip, his son by Chryseis, still a child.
Former wives of Demetrius were Stratonice of Macedon, the daughter of the Seleucid king Antiochus I, Phthia (239 BC) the daughter of Alexander of Epirus, and Nicaea, the widow of his cousin Alexander. The chronology of these marriages is a matter of dispute. From his marriage to Stratonice, he had a daughter called Apama III.
Information regarding the life of Demetrius are drawn mainly from inscription as only Plutarch writes of him, in Life of Aratus, and Polybius makes scarce mentions of him.