Simon Thassi (died 135 BCE) is the second son of Mattathias and thus a member of the Hasmonean family.

The name "Thassi" has an uncertain meaning ("the Director", "the Guide", "the Man of Counsel", and "the Zealous" are all possible meanings of the term).

He takes part in the Jewish revolt against the Seleucid Empire led by his brothers, Judas Maccabaeus and Jonathan Maccabaeus.

He becomes the first prince of the Hebrew Hasmonean Dynasty.

He reigns from 142 to 135 BCE.