| Underi | |
| Native Name: | उंदेरी |
| Location: | Raigad District, Maharashtra |
| Map Type: | India Maharashtra |
| Coordinates: | 18.7055°N 72.8413°W |
| Builder: | Siddis |
| Ownership: | Government of India |
| Open To Public: | Yes |
| Controlledby: | Siddis |
Underi (also called Jaidurg) is a fortified island near the mouth of Mumbai harbour south of Prong's Lighthouse. It is a companion fort to Khanderi and currently lies in Raigad district, Maharashtra. These islands of Khanderi and Underi served as one of the landmarks for ships entering Mumbai harbour.[1] Underi is smaller than Khanderi.
The fortification was built by Kahim of the Siddis[2] in 1680 CE. [3]