The Mengzi–Hekou railway or Menghe railway (simplified Chinese: 蒙河铁路; traditional Chinese: 蒙河鐵路; pinyin: měnghé tiělù), is a railroad in Yunnan Province of Southwest China. It is the southernmost component of the Kunming–Yuxi–Hekou railway.
The Mengzi–Hekou rail line runs 140 km (87 mi) from Mengzi City in southern Yunnan to the Hekou Yao Autonomous County on the border with Vietnam. Construction began in December 2008 and the line entered operation in December 2014.
A key element of the Mengzi–Hekou railway is the Taiyangzhai Tunnel (太阳寨隧道). The 7,414 meter-long tunnel is located in Yaoshan Township (瑶山乡) of Hekou County. Construction workers' working conditions in this tunnel have been reported as particularly difficult: with the temperature in the tunnel reaching 43°C and relative humidity 98%, it was nicknamed the "sauna tunnel" by the workers.
Drilling of this tunnel was completed in September 2013, making it possible for the entire railway project to stay on time for the completion by the end of 2014.
According to the report by Xinhua News Agency, the Mengzi–Hekou railway is to be opened on 10 December 2014 with 2 trains running from Kunming to Hekou with the maximum speed of 120 km/h and the travel time of 6 hours with the tickets sold in the following fare rates: 
- Soft sleeper fares: 182.00 [Renminbi] Yuan.
- Hard sleeper fares: 121.50 [Renminbi] Yuan.
- Seat fares: 70.50 [Renminbi] Yuan.
- Mengzi: Yuxi–Mengzi railway
- Hekou: Yunnan–Vietnam railway (via the meter-gauge connection at the Hekou North Station)
- (Chinese) "云南在建铁路项目简介" 昆明铁路局宣传部 2011-1-18
- (Chinese) 泛亚铁路东线蒙河铁路铺架开工 中国日报网 2013-01-01
- (Chinese) 蒙河铁路昨日正式开通运营 8天后或可坐火车去河口 2014-12-02
- 泛亚铁路东线蒙河铁路桑拿隧道贯通. 明年建成通车 ("Boring completed on the 'sauna tunnel' of the Mengzi–Hekou railway, the eastern section of the Trans-Asian Railway. Trains to start running by the end of the next year"), 2013-09-12
- 蒙河铁路客运开通在即 从昆明乘火车可直达中越边境 ("Passenger railway opened from Kunming by train can reach the Sino-Vietnam border"), 2014-12-09