The Northern Line (Thai: ทางรถไฟสายเหนือ) is a railway line in Thailand, running between the capital Bangkok (at Krung Thep Aphiwat Central Terminal) and the northern city of Chiang Mai (Chiang Mai railway station).

Major cities served by the line include Bangkok, Ayutthaya, Nakhon Sawan, Phitsanulok, Lampang, and Chiang Mai.

Since January 2023, long-distance (Special Express, Express and Rapid) trains terminated at Krung Thep Aphiwat Central Terminal in Bangkok replacing Hua Lamphong station.

A new 323 kilometer-long branch line, from Den Chai to the Lao border at Chiang Khong, is under construction and is expected to open in 2028.

Double-tracking has commenced between Lop Buri and Pak Nam Pho, and is planned for the rest of the line.