| En Name: | Nizhneudinsk |
| Ru Name: | Нижнеудинск |
| Coordinates: | 54.9333°N 99°W |
| Map Label Position: | right |
| Image Coa: | Nizhneudinsk COA (2019).jpg |
| Federal Subject: | Irkutsk Oblast |
| Federal Subject Ref: | [1] |
| Adm District Jur: | Nizhneudinsky District |
| Adm Ctr Of: | Nizhneudinsky District |
| Inhabloc Cat: | Town |
| Mun District Jur: | Nizhneudinsky Municipal District |
| Urban Settlement Jur: | Nizhneudinskoye Urban Settlement |
| Mun Admctr Of1: | Nizhneudinsky Municipal District |
| Mun Admctr Of2: | Nizhneudinskoye Urban Settlement |
| Area Km2: | 75 |
| Pop 2010Census: | 36999 |
| Pop Latest: | 35,500 |
| Pop Latest Date: | 2013 |
| Pop Latest Ref: | [2] |
| Established Date: | 1648 |
| Current Cat Date: | 1763 |
| Postal Codes: | 664810, 665100–665104, 665106 |
| Dialing Codes: | 39557 |
Nizhneudinsk (Russian: Нижнеу́динск|p=nʲɪʐnʲɪˈudʲɪnsk; Buriat: Доодо-Үдэ, Doodo-Üde) is a town and the administrative center of Nizhneudinsky District of Irkutsk Oblast, Russia, located on the Uda River (Yenisei's basin), 506km (314miles) northwest of Irkutsk, the administrative center of the oblast. Population: 39,700 (1970).
It was founded in 1648 and granted town status in 1783. Nizhneudinsk was so named to distinguish it from Verkhneudinsk (now Ulan-Ude).
Within the framework of administrative divisions, Nizhneudinsk serves as the administrative center of Nizhneudinsky District,[3] to which it is directly subordinated.[4] As a municipal division, the town of Nizhneudinsk is incorporated within Nizhneudinsky Municipal District as Nizhneudinskoye Urban Settlement.[5]
The town stands on the Trans-Siberian Railway and is served by a small airport, ICAO code UINN.[6]
In 1987, the 91st Motor Rifle Division was withdrawn from Mongolia and arrived at Nizhneudinsk. Later that year it became a Territorial Education Center, and then a Base for Storage of Weapons and Equipment. It was redesignated twice before becoming the 187th Base for Storage of Weapons and Equipment. The 187th Base for Storage and Repair of Weapons and Equipment of the Central Military District is based in the town.[7]
Nizhneudinsk has a subarctic climate (Köppen climate classification Dwc), with long, severely cold winters and short, warm summers. Precipitation is quite low but is much higher in summer than at other times of the year.