Lensky District (; , Lienskey 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 southwest of the republic and borders Mirninsky District in the north, Suntarsky District in the northeast, Olyokminsky District in the east, and Irkutsk Oblast in the south and west. The area of the district is . Its administrative center is the town of Lensk. As of the 2010 Census, the total population of the district was 39,765, with the population of Lensk accounting for 62.8% of that number.
The main river in the district is the Lena with its tributaries the Vitim, Peleduy, Derba and Nyuya.
Average January temperature is and average July temperature is . Annual precipitation is .
The district was established on January 30, 1930.
Within the framework of administrative divisions, Lensky District is one of the thirty-four in the republic. It is divided into one town (an administrative division with the administrative center in the town (inhabited locality) of Lensk), two settlements (administrative divisions with the administrative centers in the urban-type settlements (inhabited localities) of Peleduy and Vitim), and eight rural okrugs (naslegs), all of which comprise sixteen rural localities. As a municipal division, the district is incorporated as Lensky Municipal District. Within the municipal district, the Town of Lensk is incorporated into Lensk Urban Settlement, the two settlements are incorporated into two urban settlements, and the eight rural okrugs are incorporated into eight rural settlements. The town of Lensk serves as the administrative center of both the administrative and municipal district.
The economy of the district is mostly based on timber industry, production of construction materials, and food industry.
In the district are large oil and gas field such as :
These gas fields are the base for the Power of Siberia 1 gas pipeline linking Siberia and China.
As of the 2021 Census, the ethnic composition was as follows: