Sadyattes (reigned c.603–c.591 BC) was the third king of the Mermnad dynasty in Lydia, the son of Ardys. According to Herodotus, he reigned for twelve years. He was succeeded by his son Alyattes. Sadyattes began a war with the Ionian Greek maritime city of Miletus that was continued by Alyattes.
Dates for the Mermnad kings are uncertain and are based on a computation by J. B. Bury and Russell Meiggs (1975) who estimated c.687–c.652 BC for the reign of Gyges. Herodotus gave reign lengths for Gyges' successors: Ardys for 49 years (to c.603 BC); and Sadyattes for 12 years (to c.591 BC).
- Bury, J. B.; Meiggs, Russell (1975) [first published 1900]. A History of Greece (Fourth Edition). London: MacMillan Press. ISBN 0-333-15492-4.
- Herodotus (1975) [first published 1954]. Burn, A. R.; de Sélincourt, Aubrey (eds.). The Histories. London: Penguin Books. ISBN 0-14-051260-8.
| King of Lydia