Rathbunaster is a monospecific genus of sea stars in the family Asteriidae. The genus name was given by Walter Kenrick Fisher to honor the American biologist and administrator Richard Rathbun of the Smithsonian Institution. Rathbunaster had previously been classified in the Labidiasteridae, a family now found to be artificial. Molecular data has placed it soundly in the Asteriidae.

The only species in the genus, Rathbunaster californicus, common name California sun star, has a maximum size of about 45 centimeters in diameter and an average weight of 35 g. It lives on muddy benthic substrates between 60 and 1,000 m below the surface. it is covered in spikes with pincers that are used to capture prey for consumption.

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