The Lambir Hills National Park (Malay: Taman Negara Bukit Lambir) is a national park in Miri Division, Sarawak, Malaysia, on the island of Borneo. It is a small park, at 6,952 hectares (17,180 acres), and is composed largely of mixed dipterocarp forest, with some small areas of 'kerangas' (heath forest). The park is 150–465 m (492–1,526 ft) above sea level.

Biologists have recorded 237 species of birds, 64 species of mammals, 46 species of reptiles and 20 species of frogs in the national park. Large mammals such as gibbons and sun bear are absent or very rare due to the small size of the forest and illegal hunting. More recent surveys (2003–2007), however, failed to find 20% of the park's resident bird species and 22% of the mammal species, losses that include half of the park's primate species and six out of seven hornbill species. Collapse in population of large mammals and birds is an ecological disaster in Lambir.

The park's invertebrates include the Rajah Brooke's Birdwing butterfly (Trogonoptera brookiana) and more than 300 species of ants. Leeches are rare.

In 1991, the Sarawak Forest Department, Center for Tropical Forest Science/Harvard University, and the Plant Ecology Laboratory of Osaka City University, Japan created the Lambir Hills Forest Dynamics Plot. This is a 52-hectare (130-acre) area of the forest in which all trees thicker than 1.5 cm at breast height have been measured, mapped and identified. Every few years, researchers do a census of these trees so they can track their growth and changes in the population structure of each species. A census of all trees in the plot found 1175 different species. This gives Lambir Hills National Park possibly the highest diversity of trees of any forest in the Old World.

The dominant family of trees in the park is the Dipterocarpaceae, whose members include Shorea and Dryobalanops species. As Lambir Hills National Park is the last intact patch of lowland dipterocarp forest left in Sarawak it is an important refuge for species that have been heavily logged elsewhere.

Among the tallest trees in the national park is the tapang (Koompassia excelsa), which can grow more than 80 metres tall, and which honey bees like to build their hives on. Other interesting plants in the park include several species of Macaranga that have formed a symbiotic relationship with ants. The ants live inside the plants' hollow stems and protect them from herbivorous insects.

The pitcher plant Nepenthes hispida is found only in the park and surrounding area. The park has a very high diversity of figs (Ficus species), with nearly 80 species.

Several research institutes have collaborated on long-term studies of the Lambir's natural history and many individual MSc or PhD students have completed their fieldwork there.

In addition to the Lambir Hills Forest Dynamics Plot mentioned above, Lambir has a series of tree towers, a canopy walkway and a canopy crane that researchers use to gain access to different parts of the forest's vertical structure.

With its picturesque waterfalls, good birdwatching and impressive tall trees, the park is popular with tourists, especially at weekends when more people from Miri travel there for a day visit. For longer stays, visitors can book one of several chalets.

There are several trails for tourists to explore. These range from short and fairly flat walks to the long and sometimes steep trek to the summit of Bukit Lambir, the tallest point in the park.

• Center for Tropical Forest Science – Lambir