Mygdonia (/mɪɡˈdoʊniə/; Greek: Μυγδονία, romanized: Mygdonia) was an ancient territory, part of ancient Thrace, later conquered by Macedon, which comprised the plains around Therma (Thessalonica) together with the valleys of Klisali and Besikia, including the area of the Axios river mouth and extending as far east as Lake Bolbe.

The maritime part of Mygdonia formed a district called Amphaxitis, a distinction which first occurs in Polybius, who divides all the great plain at the head of the Thermaic gulf into Amphaxitis and Bottiaea, and which is found three centuries later in Ptolemy.

The main cities of Mygdonia were Therma (Thessalonica), Sindus, Chalastra, Altus, Strepsa, Cissus, Mellisurgis (today, Mellisourgós), and Heracleustes.

[1] Besides these, the following obscure towns occur in Ptolemy: Chaetae, Moryllus, Antigoneia (which actually refers to Antigonia Psaphara in the Chalcidice[2]), Calindaea, Boerus, Physca, Trepilus, Carabia, Xylopolis, Assorus, Lete, Phileres, Dicaea, Aeneia and Arethusa .

[3] Paeonians and also Thracians (in particular, the Edonians) ruled and inhabited the region for a time, until it was annexed to Macedon.