Eubranchus steinbecki is a species of sea slug or nudibranch, a marine gastropod mollusc in the family Eubranchidae.
This species was described from specimens collected from boat floats at Dana Landing, Mission Bay, San Diego, and intertidally at Malibu, , California, United States. It has been reported from Palos Verdes south to La Paz, Baja California Sur, Mexico.