Mbaracayú Forest Nature Reserve, Nature reserve in Canindeyú, Paraguay.

Mbaracayú Forest Nature Reserve is a large protected area of humid subtropical forest with deep valleys, waterfalls, and streams that feed into the Jejuí River. The landscape varies from steep hillsides to flat areas, creating different habitats throughout the reserve.

The reserve was created by an agreement among Paraguay's government, the Moisés Bertoni Foundation, UNESCO and The Nature Conservancy, ratified in 1991 by National Law 112/91. It was declared a Paraguayan heritage area dedicated in perpetuity to protecting forest, biodiversity and cultural resources. On 19 December 2003 it was submitted to UNESCO as a proposed World Heritage Site.

The reserve's name comes from the Mbaracayú range crossing its northeastern corner, and the land is managed by the Moisés Bertoni Foundation, a Paraguayan NGO named after the Swiss-Paraguayan naturalist Moisés Bertoni. Law 112/91 designated the area a Paraguayan heritage site dedicated to forest, biodiversity and cultural resources, and it was proposed to UNESCO on 19 December 2003.

The reserve lies in the upper Jejuí Guazú basin, surrounded by cattle ranches and small farms, so access is overland through private farmland. The Cordillera de Mbaracayú crosses the northeastern corner, where small deep valleys carry streams and waterfalls. Rainfall averages 1,800 mm a year and the area floods periodically, so low ground near the Jejuí is wettest in the wet summer, when temperatures reach 42 °C; dry winter nights can fall to −2 °C.

Parts of the forest stay permanently flooded, creating a special habitat where caimans and other water creatures thrive in conditions found nowhere else in the region. These waterlogged areas support a completely different ecosystem than the rest of the reserve.