Ría Lagartos Biosphere Reserve () (established 2004) is a UNESCO Biosphere Reserve in the state of Yucatán, Mexico. The reserve is located at the eastern end of the coastal strip of the Yucatán Peninsula, with the Gulf of Mexico at its northern limit. The area encompasses coastal areas of the Gulf of Mexico and includes important wetlands designated under the Ramsar Wetlands Convention. The site presents a rich diversity of landscapes and ecosystems, such as mangroves, small estuaries, medium semi-evergreen forest, low deciduous forest, coastal dune vegetation, coastal lagoons, marshes ("petenes") and savanna represented by tular vegetation, grasslands and reed beds that are the main nesting sites for marshland and sea birds.