Dionysius of Miletus was a Greek historian of the 5th century BCE, active in the period following the Greco-Persian Wars. A contemporary of Hellanicus of Lesbos and slightly older than Herodotus, his epithet identifies him with the Ionian city of Miletus, a center of early historiography. No further biographical details are recorded.

His sole known work is the Persica, a history of Persia. The work is now lost and survives only in fragments and testimonia.

Dionysius is significant as one of the earliest Greek logographers, or prose historians, preceding Herodotus. His Persica represents an early Greek ethnographical and historical focus on the Persian Empire, placing him within the first generation of historians and the Ionian tradition of inquiry that contributed to the development of historiography.