Eubranchus olivaceus is a species of sea slug or nudibranch, a marine gastropod mollusc in the family Eubranchidae.

[2] This species was described from Jesse Island and Brandon Island, Departure Bay, and the biological research station at Nanaimo, Vancouver Island, Canada.

It is considered by some authors to be a synonym of the North Atlantic species Eubranchus rupium.

[3] In the original description Eubranchus olivaceus is reported to feed on Obelia longissima.

It is also reported to feed on the hydroids Laomedea flexuosa, Obelia spp., & Plumularia sp.