Cát Bà National Park is a World Heritage Site designated as a biosphere reserve in northern Vietnam. The park is part of Cát Bà Island in Hạ Long Bay and is administered by the city of Haiphong. The park is located approximately 30 kilometres (19 mi) east of Hai Phong, covering about 263 square kilometres (102 sq mi) and comprising 173 square kilometres (67 sq mi) of land and 90 square kilometres (35 sq mi) of inshore water.
The Cát Bà langur, also known as the white-headed langur (Trachypithecus poliocephalus) is resident within the park and is classified by the International Union for Conservation of Nature as a critically endangered primate; one of the rarest in the world.
Cát Bà National Park was established on 31 March 1986 under No.79/CP decision of the Council of Ministers of Vietnam (now the government). The park has been a popular tourist destination, since the mid-1990s with wealthy Chinese and Vietnamese tourists. The tourists created a demand for traditional medicine and development and logging led to the near extinction of the white-headed langur with numbers falling from 2600 to just 40 in 2003. In 2016 there are 67 (± 5).