Mamontovsky District () is an administrative and municipal district (raion), one of the fifty-nine in Altai Krai, Russia. It is located in the center of the krai. The area of the district is . Its administrative center is the rural locality (a selo) of Mamontovo. As of the 2010 Census, the total population of the district was 23,412, with the population of Mamontovo accounting for 37.5% of that number.
Lakes Gorkoye and Bolshoye Ostrovnoye are located in the district.