Diodotus II (flourished 3rd century bc) was the king of Bactria, the son and successor of Diodotus I.
Although his father’s freedom from Seleucid control is uncertain, Diodotus II unquestionably ruled as an independent king and issued coinage in his own name. He further proclaimed the independence of the kingdom of Bactria by entering into an alliance with the Parthians against Seleucus II, in contrast with his father’s friendly policy toward the Seleucid Kingdom. At an uncertain date (perhaps c. 235), Diodotus II was overthrown by the usurper Euthydemus.