Sindhudurg (Marathi: सिंधुदुर्ग जिल्हा) is an administrative district in the state of Maharashtra in India, which was carved out of the erstwhile Ratnagiri District. The district headquarters are located at Oros (ओरस). The district occupies an area of 5207 km² and has a population of 868,825 of which 9.47% were urban (as of 2001).
As of 2011 it is the least populous district of Maharashtra (out of 39).
The district is named after the fort of Sindhudurg (which means "fort in the sea"), which lies on a rocky island just off the coast of Malvan. Sindhudurg fort, built in the 16th century by Shivaji is the only fort which has Shivaji temple inside the fort and palm imprint of King Shivaji. Sindhudurg district has 37 forts, the highest number of forts in Maharashtra as well as all types of forts (Jaldurg – Sea), (Bhuikot – fort on land) and (Giri- fort on hilltop).