Ranganthittu Bird Sanctuary (Kannada: ರಂಗನತಿಟ್ಟು ಪಕ್ಷಿಧಾಮ) is a Bird Sanctuary in the Mandya District of the state of Karnataka in India. It is a very small sanctuary, being only 0.67 km². in area, and comprises six islets on the banks of the Kaveri River. Ranganthittu is located near the historic town of Srirangapatna.

The islets came into being when a dam across the Kaveri river was built in the 1700s. The ornithologist Dr. Salim Ali observed that the isles formed an important nesting ground for birds, and persuaded the Wodeyar kings of Mysore to declare the area a wildlife sanctuary in 1940.

Riverine reed beds cover the banks of the islands, while the islands themselves are covered in broadleaf forests, with dominant species being Terminalia arjun (Arjun tree), bamboo groves, and Pandanus trees. Eucalyptus and Acacia trees have also been planted, which might lead to long-term eradication of native species. The endemic and threatened lily Iphigenia mysorensis of the family Colchicaceae grows in the sanctuary.

The islands are host to numerous small mammals, including Bonnet Macaque, colonies of Flying Fox and common small mammals like Common Palm Civet and Indian Gray Mongoose and the monitor lizard.

The Mugger Crocodile or Marsh Crocodile is a common inhabitant of the riverine reed beds. Breeding water birds include Painted Stork, Asian Openbill Stork, Common Spoonbill, Woolly-necked Stork, Black-headed Ibis, White Ibis, Lesser Whistling Duck, Indian Shag, Stork-billed Kingfisher and other common birds like egrets, cormorants, Oriental Darter, and herons. The Great Stone Plover, and River Tern also nest here. The park is home to a large flock of Streak-throated Swallows.

Ranger-guided boat tours of the isles are available throughout the day, and are a good way to watch birds, crocodiles, otters and bats. There is no lodging at the tiny sanctuary, so visitors typically have to stay over at Mysore or Srirangapatna. The seasons for visiting the park are: June - November (during the nesting season of the water birds). The best time to watch migratory birds is usually December but it can vary year to year. In 2007 as of mid-December migratory birds had not yet arrived.