Apantesis elongata is a moth of the family Erebidae. It was described by in 1885. It is found in south-western British Columbia and west-central Alberta, south to Montana and Washington. It has also been recorded from north-eastern Oregon. The habitat consists of dry, montane, and subalpine meadows. The length of the forewings is 14.9 mm. The ground colour of the forewings is brownish black. The hindwings are pale yellowish white in males and yellow in females. Adults are on wing from mid May to late August. The larvae have been recorded feeding on Claytonia lanceolata.