FR235222, a novel immunosuppressant which possesses potent inhibitory effects on the activity of mammalian histone deacetylases (HDACs), has been isolated from the fermentation broth of a fungus, Acremonium sp. No. 27082. FR235222 exhibited marked immunosuppressive effects on mouse ex vivo splenic T-lymphocyte proliferation, mouse delayed type hypersensitivity (DTH) response, rat adjuvant-induced arthritis (AA) and rat heterotopic cardiac transplantation. These results showed potential clinical use of this compound as a new type immunosuppressant in the fields of autoimmune diseases and organ transplantations.