Tianmu Mountain, Mount Tianmu, or Tianmushan is a mountain in Lin'an County 83.2 kilometers (51.7 mi) west of Hangzhou, Zhejiang, in eastern China. It is made up of two peaks: West Tianmu (1,506 meters or 4,941 feet) and East Tianmu (1,480 meters or 4,860 feet). Twin ponds near the top of the peaks led to the name of the mountain. China's Tianmu Mountain National Nature Reserve lies on the northwest portion of the mountain. It is a UNESCO Biosphere Reserve as part of UNESCO's Man and the Biosphere Program. The mountain has a lush sub-tropical climate with an annual rainfall of 1,767 millimeters (69.6 in) and an annual temperature of 17.3 °C (63 °F).
Tianmu is known for giant Japanese cedars, waterfalls, Tianmu tea, peaks surrounded by clouds, bamboo shoots, temples and nunneries, and odd-shaped rocks. More than 2,000 species of plants grow on the mountain, including (on West Tianmu) the last surviving truly wild population of Ginkgo trees. Prominent among the Japanese cedars is the "Giant Tree King", named by the Qianlong Emperor of the Qing. In 2009, it measured 26.5 meters (86 ft 11 in) in height, 2.33 meters (7 ft 8 in) in diameter, and 42.9 cubic meters (1,510 cu ft) in volume. The mountain is also home to hundreds of species of birds and animals, including 39 endangered or protected species. These include the clouded leopard and the black muntjac.
In Chinese, the name Tianmushan can also refer to the adjacent range of mountains, including Mount Mogan.