|Native name: Μεγαλονήσι|
|Coordinates||34°55′23″N 24°48′00″E / 34.923°N 24.8°ECoordinates: 34°55′23″N 24°48′00″E / 34.923°N 24.8°E|
Megalonisi (Greek: Μεγαλονήσι, "big island") is an islet off the southern coast of the Greek island of Crete in the Libyan Sea that hosts a lighthouse. The islet is in a bay between the capes of Lithino and Kefalas, at Kommos, and close to Gortyn which was the ancient capital of Crete. It is administered within Heraklion regional unit.