Cleombrotus I (died July 6, 371 BCE) is a Spartan king of the Agiad line, reigning from 380 BCE until 371 BCE.

Little is known of Cleombrotus' early life.

The son of Pausanias, he becomes king of Sparta after the death of his brother Agesipolis I in 380 BCE, and leads the allied Spartan-Peloponnesian army against the Thebans under Epaminondas in the Battle of Leuctra.

His death and the utter defeat of his army lead to the end of Spartan dominance in ancient Greece.

Cleombrotus is succeeded by his son Agesipolis II.

His other son is Cleomenes II.