| Orkhon River | |
| Name Other: | Mongolian: Orkhon Gol |
| Subdivision Type1: | Country |
| Subdivision Name1: | Mongolia |
| Subdivision Type2: | Aimags |
| Subdivision Name2: | Övörkhangai, Arkhangai, Bulgan, Darkhan-Uul, Selenge |
| Subdivision Type5: | Major cities |
| Subdivision Name5: | Kharkhorin (Karakorum), Sükhbaatar |
| Length: | 1124km (698miles) |
| Discharge1 Location: | Bulgan |
| Discharge1 Min: | 0.5m3/sFebruary |
| Discharge1 Avg: | 66m3/s |
| Discharge1 Max: | 190.2m3/sJuly |
| Source1: | Suvraga Khairkhan |
| Source1 Location: | Tsenkher sum, Arkhangai |
| Source1 Coordinates: | 47.0497°N 101.3417°W |
| Mouth: | Selenga |
| Mouth Location: | Sükhbaatar city, Selenge aimag |
| Mouth Coordinates: | 50.25°N 106.1389°W |
| Basin Size: | 132835km2 |
| Tributaries Left: | Tamir River |
| Tributaries Right: | Tuul River, Kharaa River |
The Orkhon River (; Mongolian: Орхон гол in Mongolian pronounced as /ˈɔrχɞɴ‿ɢɜɮ/) is a river in Mongolia.
The Orkhon river derives its name from the Old Turkic prefix "or" meaning "middle", and "khan" or king.
It rises in the Khangai Mountains in the Tsenkher sum of Arkhangai aimag at the foot of the Suvraga Khairkhan mountain.[1] From there, it crosses the border into Övörkhangai aimag and follows the upper Orkhon valley in an eastern direction until it reaches Kharkhorin. On this stretch, very close to the Orkhon, the Ulaan Tsutgalan river features a waterfall, 10abbr=outNaNabbr=out wide and 20abbr=outNaNabbr=out high,[2] which is a popular destination for tourists.
From Kharkhorin it flows northwards until it reaches Bulgan aimag, and then north-east to join the Selenge River next to Sükhbaatar city in Selenge aimag, close to the Russian border.[3] The Selenge then flows further north into Russia and Lake Baikal.
With 1124km (698miles), the Orkhon is longer than the Selenge, making it the longest river in Mongolia. Major tributaries of the Orkhon river are the Tuul River and Tamir River.
There are two sets of ancient ruins along the river valley: Khar Balgas, the ancient capital of the Uyghur Kingdom and Karakorum, the ancient capital of the Mongol Empire. Pyotr Kuzmich Kozlov excavated several Xiongnu Imperial tombs in the area of the river valley.
Fish in the Orkhon River include pike, carp, perch, taimen and catfish.
UNESCO lists the Orkhon Valley as a World Heritage Site.