Ust-Olenyok (; ) is a rural locality (a selo), the only inhabited locality, and the administrative center of Ystannakhsky Rural Okrug of Bulunsky District in the Sakha Republic, Russia, located from Tiksi, the administrative center of the district. Its population as of the 2010 Census was 27, down from 52 recorded during the 2002 Census.
The settlement is located on the slope of a low hill, by the right bank of the mouth of the Olenyok River. The confluence of the Buolkalakh is located about upstream on the facing bank.
The first settlement was a wintering hut built in 1633 near the modern village. It served as the administrative center of the desolate area and it was used by several Arctic expeditions.
Ust-Olenyok has a tundra climate (ET) with short, cool summers and long, severely cold winters. On June 30, 2020, the temperature soared to 93.7 ðF (34.3 ðC) which may be the farthest north above 90 ðF (32.2 ðC) recorded above the 72 ðN parallel. The following morning the temperature only dropped to 72.7 ðF (22.6 ðC).