Eubranchus rupium, the green balloon aeolid, is a species of sea slug or nudibranch, a marine gastropod mollusc in the family Eubranchidae.

[2] This species was described from Greenland.

It is reported from the North Atlantic Ocean as far south as the Netherlands and is considered to be a circumpolar species.

It is considered by most authors to be a synonym of Eubranchus olivaceus and is reported as far south as Monterey Bay, California on the Pacific Ocean coast of North America.

[3][4][5] This nudibranch feeds on the hydroids Laomedea longissima.