Ononsky District () is an administrative and municipal district (raion), one of the thirty-one in Zabaykalsky Krai, Russia. It is located in the south of the krai, and borders Aginsky District in the north, Borzinsky District in the east, and Akshinsky District in the west. The area of the district is . Its administrative center is the rural locality (a selo) of Nizhny Tsasuchey. As of the 2010 Census, the total population of the district was 11,199, with the population of Nizhny Tsasuchey accounting for 30.0% of that number.
The district was established on February 5, 1941.