El Cielo Biosphere Reserve is the southern part of the state of Tamaulipas in northeast Mexico. It is a designated UNESCO Biosphere Reserve.
This protected biosphere reserve is in a mountainous area of southern Tamaulipas in the Sierra de Cucharas, part of the Sierra Madre Oriental range. It is an ecologically diverse area with 14 vegetation types (mostly tropical forest), though the most important goal is to preserve the mountainous cloud forest because it is a rarer ecology in Mexico and is the furthest north example of this environment. The reserve provides habitat for a number of endemic and threatened plant and animal species. Large mammals who make their home in the reserve include black bears, tigrillos (leapardus wiedii), jaguars, and ocelots. 255 bird species have been cataloged in the reserve, along with dozens of reptile species.
The reserve covers an area of 144,530 hectares. El Cielo is a designated UNESCO biosphere reserve.
The reserve was founded in 1935 by a Canadian horticulturist named John Harrison.
Several cabins and basic hotels are on state highway 58 as it passes through the town of Gomez Farias adjacent to the biosphere reserve.