Amadocus (Greek: Ἀμάδoκoς; lived 4th century BC) was a ruler in Thrace, who inherited in conjunction with Berisades and Cersobleptes the dominions of Cotys, on the death of the latter in 358 BC. Amadocus was probably a son of Cotys and a brother of the other two princes, though this is not stated by Demosthenes. The area controlled by Amadocus was west of the river Hebrus.
When Cersobleptes negotiated with Philip II of Macedonia for a combined attack on the Chersonese, Amadocus refused to allow Philip passage through his territory, in consequence of which the scheme came to nothing.
Both Amadocus and Cersobleptes appear to have been subjected by Philip early in 347 BC, not long after Cetriporis, the son and successor of Berisades, suffered the same fate. The two rulers, having appealed to the Macedonian ruler to arbitrate a dispute between them, were then been forced to acknowledge his suzereinty when the "judge" showed up with an army.
Amadocus seems to have had a son of the same name. His successor, however, appears to have been Teres III.