Ust-Aldansky District (; , Uus-Aldan uluuha, ) is an administrative and municipal district (raion, or ulus), one of the thirty-four in the Sakha Republic, Russia. It is located in the center of the republic and borders with Kobyaysky District in the north, Tomponsky District in the northeast, Tattinsky District in the east, Churapchinsky District in the southeast, Megino-Kangalassky District in the south, and with Namsky District in the west. The area of the district is . Its administrative center is the rural locality (a selo) of Borogontsy. Population: 22,372 (2002 Census); The population of Borogontsy accounts for 23.6% of the district's total population.
The landscape of the district is mostly flat. Its main rivers include the Lena and the Aldan. There are many lakes in the district, the largest of which are Lakes Myuryu, Oner, and Targyldzhyma.
The district was established on January 9, 1930.
As of the 2021 Census, the ethnic composition was as follows:
The economy of the district is mostly based on agriculture.
<small>Divisional source:</small><br /> <br/> <small>*Administrative centers are shown in bold</small>