The Titiwangsa Mountains (Malay: Banjaran Titiwangsa, pronounced [ˈband͡ʒaˈran titiwaŋˈsa]), also known as Banjaran Besar (lit. 'main range') by locals, is the chain of mountains that forms the backbone of the Malay Peninsula. The northern section of the range is in southern Thailand, where it is known as the Sankalakhiri Range (Thai: ทิวเขาสันกาลาคีรี; RTGS: Thio Khao Sankalakhiri; pronounced [tʰīw kʰǎw sǎn.kāːlāːkʰīːrīː]).

The mountain range acts as a natural divider, dividing Peninsular Malaysia, as well as southernmost Thailand, into east and west coast regions. It also serves as a drainage divide of some major rivers of Peninsular Malaysia such as the Pahang, Perak, Kelantan, Klang and Muar. The length of mountain range is about 480 km from north to south.

This mountain range is a part of the wider Tenasserim Hills. It forms the southernmost section of the Indo-Malayan cordillera which runs from Tibet through the Kra Isthmus into the Malay Peninsula.

The Titiwangsa Mountains proper begin in the north as the Sankalakhiri Range, a prolongation of the Nakhon Si Thammarat Range which includes the smaller Pattani, Taluban, and Songkhla sub-ranges. The Sankalakhiri marks the border between the Southern Thai provinces of Yala in west and Narathiwat in the east. Across the border into Malaysia, the main stretch of the range runs in a northwest–southeast orientation, straddling the borders between the west coast states of Perak and Selangor with Kelantan and Pahang on the eastern side of the peninsula. From the tripoint of Pahang, Selangor and Negeri Sembilan near Mount Nuang, it then transverses through the middle of the state of Negeri Sembilan, also a west coast state, thus dividing the state into two regions – western Negeri Sembilan, which consists of Seremban, Port Dickson and Rembau Districts, and eastern Negeri Sembilan, composed of the districts of Jelebu, Kuala Pilah, Jempol and Tampin – and terminates in the south near the town of Tampin, in the southern part of the state. Outcrops of Titiwangsa granite, mainly consisting of inselbergs, project further south into Malacca, where it abuts in the waters of the Strait of Malacca in Pulau Besar.

In general, the greatest elevations occur along the northern and central sections of the range, with its highest point measuring 2,183 m (7,162 ft) on Gunung Korbu, Perak. On the Thai side, the highest point is 1,533 m (5,026 ft) Ulu Titi Basah (ยูลูติติ บาซาห์), at the Thai/Malaysian border between Yala province and Perak. On the other hand, the height gradually diminishes towards the southern reaches of the range, which mainly runs through Negeri Sembilan, with elevations ranging from 1,462 m (4,797 ft) at its highest on Mount Besar Hantu, on the border between the state and Pahang, as well as 1,193 m (3,914 ft) on Mount Telapak Buruk on the boundary between the districts of Seremban and Jelebu to 500–900 metres (1,600–3,000 ft).

The Titiwangsa Mountains are predominantly granitic. The mountain range is part of a suture zone that runs north–south, starting in Thailand at the Nan-Uttaradit suture zone (partly coincident with the Dien Bien Phu fault), and extending south towards Peninsular Malaysia (Bentong-Raub suture zone). The eastern half of the Titiwangsa Mountains in Peninsular Malaysia is an amalgamation of continental terranes known as Cimmeria or Indochina, whereas the western half is an amalgamation of continental terranes Sinoburmalaya or Sibumasu. These two halves of terranes were separated by the Paleo-Tethys Ocean.

The Cimmeria was separated from Gondwana around 400 mya during the Devonian and rifted towards Laurasia, the northeastern arm of Pangea. It attached to Laurasia completely around 280 mya during the Late Permian.

Sibumasu terranes on the other hand, only started to separate from Gondwana during the Early Permian and rifted towards Indochina. The collision of the Sibumasu terranes and Indochina terranes 200 mya during the Late Triassic resulted in the closure of the Paleo-Tethys Ocean and formation of the modern Titiwangsa Mountain belts.