Ptolemy of Megalopolis was a Greek historian from Arcadia, active during the Hellenistic period in the 3rd or 2nd century BCE. No details of his personal life or education survive.

His sole known work is On Philopator, a history concerning Ptolemy IV Philopator of Egypt. The text is lost, preserved only in fragments cited by later authors.

Ptolemy is a minor historian whose significance derives from his work being used as a source for the reign of Ptolemy IV. His fragments, cited by compilers like Athenaeus, represent one of many lost Hellenistic histories utilized by later tradition.