The Bukit Timah Nature Reserve (abbreviation: BTNR) is a nature reserve near the geographic centre of Singapore. It is located on the slopes of Bukit Timah Hill, the country's highest natural peak standing at approximately 165 metres (541 ft), and includes parts of the surrounding area within the planning area of Bukit Panjang. The nature reserve sits about 15 kilometres (9.3 miles) north-west from the Central Area, Singapore's city-centre, and is roughly 2 km² (0.77 sq mi) in size.

Together with the neighbouring Central Catchment Nature Reserve (CCNR) in close proximity, it houses over 840 species of flowering plants and over 500 species of fauna. Today, it is one of the largest patches of primary rainforest left in Singapore. The forest reserve was formally declared as an ASEAN Heritage Park on 18 October 2011.

The name Bukit Timah is borrowed from the tallest hill found in the area of the same name, which is also the tallest geographical location in all of Singapore. Bukit means hill in the Malay language, while Timah means tin. It is directly translated to English as "Tin Hill".

The hill served as a granite quarry for many years, but since the mid-1900s, all quarrying operations have been abandoned and the area converted into recreational and even filming locations.

In 1882, Nathaniel Cantley, the Superintendent of the Singapore Botanic Gardens, was tasked with assessing the forests of the Straits Settlements. His recommendations led to the creation of several forest reserves, including Bukit Timah in 1883. While most reserves were exploited for timber, Bukit Timah was preserved. By 1937, many reserves were depleted due to development pressures, but Bukit Timah and two other areas remained protected for their flora and fauna. In 1951, the Nature Reserves Ordinance established formal protection for these areas, which were then managed by the Nature Reserves Board. Today, under the National Parks Act and managed by the National Parks Board, these nature reserves continue to safeguard Singapore's indigenous flora and fauna.

The primary activities at Bukit Timah are strolling, running and hiking. There are also smaller groups of people who rock-climb and abseil at the Dairy Farm quarry as well as mountain biking. There are specially-allocated mountain-bike trails around the area and Bukit Timah Mountain Bike (MTB) Trail is located within the Reserve. The 6.5 km MTB trail loop around Bukit Timah Hill and stretched between Hinhinde Park and Dairy Farm Road. The trail represents a tropical rocky terrain with extended technical climbs and difficult descents at short intervals. For MTB Map trail rating, it is largely made up of black diamond sections with intermittent blue square sections. There are also short alternative double black diamond sections.

The Reserve is popular among athletes training for mountain-climbing. There are a number of hiking trails. The blue trail is rated as "easy" and is 0.7 kilometres (0.43 mi) long, ending overlooking Hindhede Quarry. The red trail is also rated as "easy" and is 1.2 kilometres (0.75 mi) long. The green trail is rated as "moderate to difficult" and is 1.9 kilometres (1.2 mi) long. The yellow trail is rated as "difficult" and is 1.8 kilometres (1.1 mi) long. The red, green and yellow trails all end at the hut at the summit of Bukit Timah hill.

The park has been designated with the code 9V-0007 by the international Parks On The Air award program, and so is regularly 'activated' by Amateur Radio operators using portable equipment.