Aetiocetidae is an extinct family of toothed baleen whales known from the Oligocene and latest Eocene, so far only from rocks deposited in the North Pacific Ocean.

[3][4][5] The whales ranged in size from 3 to 8 metres (10 to 26 ft) long.

Other formally described extinct toothed mysticetis from this time are smaller, from 3 to 4 metres (10 to 13 ft) in length.

Mysticeti with true baleen are seen in fossils from the Upper Oligocene.

The monophyly of the family is still uncertain, as are the evolutionary relationship between the early toothed baleen whales (Aetiocetidae, Mammalodontidae, and Llanocetidae) and the early and extant edentulous baleen whales.