A 23-year-old captive female California sea lion (Zalophus californianus) developed an inferiotemporal subconjunctival swelling of the right eye. Surgical excision of the mass was performed and a diagnosis of orbital fat prolapse was confirmed histopathologically. There was no recurrence of orbital fat prolapse at 15 months post operatively. This is the first known case of orbital fat prolapse in the California sea lion.