Ust-Olenyok (Russian: Усть-Оленёк; Yakut: Уус Өлөөн / Ыстааннаах, romanized: Ûs Ölöön / Istânnâx) 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 365 kilometers (227 mi) from Tiksi, the administrative center of the district.

[1] 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 9 km (5.6 mi) upstream on the facing bank.

It served as the administrative center of the desolate area and it was used by Arctic expeditions in different occasions in history.

[7] Ust-Olenyok has a tundra climate (ET) with short, cool summers and long, severely cold winters.