Aurilide (1), a new 26-membered cyclodepsipeptide, has been isolated from the Japanese sea hare Dolabella auricularia. The gross structure of 1 was established by spectroscopic analysis. The absolute stereostructure of 1 was determined by HPLC analysis of amino acid components and isoleucic acid obtained from acidic hydrolysis of 1 and by the enantioselective synthesis of the tris(p-bromobenzoate) 3 derived from the dihydroxy acid moiety.