| Cleomenes III | |
|---|---|
| King of Sparta | |
 Kings Agis and Cleomenes, late 17th century engraving. | |
| Reign | 235–222 BC |
| Predecessor | Leonidas II |
| Successor | Agesipolis III |
| Born | c. 265–260 BC Sparta |
| Died | 219 BC Alexandria |
| Consort | Agiatis |
| Issue | Unknown (at least one son) |
| Dynasty | Agiad |
| Father | Leonidas II |
| Mother | Cratesiclea |
Cleomenes III (Ancient Greek: Κλεομένης) was one of the two kings of Sparta from 235 to 222 BC. He was a member of the Agiad dynasty and succeeded his father, Leonidas II. He is known for his attempts to reform the Spartan state.
From 229 to 222 BC, Cleomenes waged war against the Achaean League under Aratus of Sicyon. After being defeated by the Achaeans in the Battle of Sellasia in 222 BC, he fled to Ptolemaic Egypt. After a failed revolt in 219 BC, he committed suicide.