ruler of Syracuse, in Sicily, 367–357 and 346–344 BC.

Dionysius was the son and successor of Dionysius I, but he lacked the vigour to maintain the military autocracy he had inherited. Upon his accession in 367 he made peace with Carthage on the same unfavourable terms established after his father's defeat in the third war with Carthage (383–c. 375). Dion, a former minister, tried with Plato to make a philosopher-prince of Dionysius, but both counselors were dismissed in 366. In 357 Dion drove Dionysius from his kingdom, and the deposed ruler fled to Locri. In 346, some eight years after the assassination of Dion, Dionysius regained control of Syracuse. On the arrival of the Greek general Timoleon of Corinth two years later, Dionysius was compelled to surrender and retire to Corinth.