Khun Tan Tunnel (Thai: อุโมงค์ขุนตาน) is the longest of Thailand's seven railway tunnels. It is 1352.10 metres long, and situated between kilometre 681.57870 and 682.94080 on the Northern line from Bangkok to Chiang Mai, between Ma Tan Noi and Khun Tan stations [1]. The tunnel runs under the boundary between Lampang and Lamphun provinces.