Dionysius Thrax (Διονυσιος Θραξ) (170 BC‑90 BC) is a Greek grammarian who lived and is thought by some to have worked in Alexandria and later at Rhodes.

He collected the knowledge of the time on language and grammar. His main work on language is "Tekhné grammatiké", a work that became a standard manual of syntax for over 1,000 years.